RFQ Today
Certifications available: EN 10204 3.1 / 3.2 MTRs, NACE MR0175 compliance, Third-Party Inspection witness, ASTM / DIN / ISO / BS standards, and complete EPC export documentation packages.
Machine Screws
A world-class technical reference for EPC contractors, mechanical and instrumentation engineers, procurement heads, TPI inspection agencies, and global project buyers specifying machine screws in precision assemblies, instrumentation panels, enclosures, equipment housings, valve actuators, and industrial machinery across Oil & Gas, Power Generation, Petrochemical, Aerospace, and Electronic Manufacturing sectors.
Drive Systems &
Load Characteristics
Machine screws are externally threaded fasteners designed to be driven into pre-tapped holes or used with nuts, characterised by their small diameter range (typically M1.6 to M12 or #0 to ¼” UNC), precision thread forms, and varied head profiles with standardised drive recesses. They are fundamental fasteners in instrumentation, control panels, valve actuators, enclosures, equipment assembly, and precision mechanical systems throughout the EPC, Oil & Gas, and industrial manufacturing sectors.
1.1 — Technical Definition and Functional Role in EPC and Industrial Systems
A machine screw is a fully threaded fastener with a formed head and a standardised drive recess (slot, Phillips, Pozidriv, hexagon socket, Torx, or combination), designed for use in tapped holes in metal, plastic, or composite components. Unlike bolts (which require a nut and through-hole) or self-tapping screws (which form their own thread), machine screws engage a pre-machined or pre-formed thread with a defined fit class — providing a precision, repeatable, and calculable clamping force for the assembled joint.
In EPC and industrial environments, machine screws appear in: electrical and instrument panel assembly, control valve actuator covers and end-caps, junction box and enclosure mounting, pump and compressor inspection covers, heat exchanger bonnet fastening (small bore), pressure gauge and transmitter mounting, motor terminal box covers, solenoid valve body assembly, and precision machinery adjustment mechanisms. Their correct specification — covering head type, drive recess, grade, material, coating, and thread class — directly determines assembly integrity, torque performance, and service reliability.
RR Hydraulic manufactures and exports machine screws to global EPC and industrial projects under all applicable international standards with EN 10204 3.1 / 3.2 material traceability and full project documentation capability.
1.2 — Head Type Classification
Pan Head
Slightly rounded top surface with a flat bearing face and cylindrical sides. Provides a large bearing area on the assembled surface. The most common general-purpose machine screw head. Per ISO 14583 (Torx), ISO 7045 (Phillips/Pozi), DIN 7985. Preferred for most panel, enclosure, and instrument assembly applications.
Countersunk (Flat) Head
90° or 82° conical underside designed to sit flush with or below the assembled surface when inserted into a countersunk hole. Per ISO 2009 (slotted), ISO 7046 (Phillips), DIN 963, DIN 965. Used where a flush surface is required for safety, aerodynamics, aesthetics, or to prevent snagging on adjacent components or cables.
Raised Countersunk (Oval) Head
Conical countersunk underside with a low dome above the surface — combines the flush fit of a countersunk head with a finished dome appearance above the surface. Per ISO 2010 (slotted), ISO 7047 (Phillips/Pozi), DIN 966. Used in decorative panels, instrument faces, and visible assemblies where aesthetics matter.
Cheese Head
Cylindrical head with a flat top and flat bearing face — larger head diameter than pan head relative to the same thread size, providing maximum bearing area and torque capacity. Per ISO 1207 (slotted), DIN 84. Preferred in heavy machinery and industrial applications where maximum clamp load for the thread size is required.
Fillister (Slot) Head
Deep cylindrical head with a flat top and a relatively deep slot — the tall head allows a large slot depth, providing high torque transmission capacity from a slotted driver. Per ASME B18.6.3. Common in legacy electrical panel work and instrument assemblies in North American EPC projects where slotted screws remain specified.
Binding Head
Wide, flat cylindrical head with a slight undercut to the bearing face — originally designed for electrical wiring work where the undercut retains wire insulation under the head. Per ASME B18.6.3. Used in terminal block assemblies, electrical panels, and wiring harness attachments in EPC electrical and instrumentation scopes.
Truss Head
Extra-wide, low-profile domed head — maximum bearing area with minimum height above the surface. Prevents pull-through in thin sheet metal or soft material assemblies. Per ASME B18.6.3. Used in thin-gauge enclosure assembly, control panel backing, and electrical trunking attachments where a standard pan head would crush or pull through the sheet material.
Hex Head Machine Screw
Hexagonal head for wrench drive — same as a hex cap screw but in the small-diameter machine screw size range. Provides the highest torque capacity of all machine screw head types; preferred where high clamping force is required or where the assembled material is hard (steel to steel) and slippage of a recessed driver is unacceptable. Per ISO 4017 (small sizes), DIN 933.
1.3 — Drive Recess Systems: Engineering Selection
| Drive Type | Standard | Cam-Out Risk | Torque Capacity | Tool Type | Tamper Resistance | Primary Application |
|---|---|---|---|---|---|---|
| Slotted | ISO 2009 / ASME B18.6.3 | High | Low | Flat screwdriver | None | Legacy electrical, panel trim — avoid in new designs |
| Phillips (PH) | ISO 7045 / ASME B18.6.3 | Moderate (by design) | Moderate | Phillips screwdriver PH0–PH4 | None | General assembly, sheet metal, enclosures |
| Pozidriv (PZ) | ISO 4757 / DIN 4757 | Low | Moderate–High | Pozidriv screwdriver PZ0–PZ4 | None | European EPC assembly, instrument panels |
| Hex Socket (Allen) | ISO 4762 / DIN 912 | None (non-cam) | High | Hex key / ball-driver | Low (standard) | Machinery, precision instruments, valves |
| Torx (TX) | ISO 14583 / DIN 7985-TX | None | Very High | Torx bit T6–T40 | Low (standard) | Automotive, electronics, precision panels |
| Torx Plus (IP) | Proprietary (Acument) | None | Highest | Torx Plus bit | Low | High-torque precision; aerospace, instrumentation |
| Security Torx (TR) | Proprietary | None | Very High | Security Torx bit | High | Tamper-proof panels, controlled access enclosures |
| Combination (PH+Slot) | ASME B18.6.3 | Moderate | Moderate | Either Phillips or flat | None | Field service accessibility — multiple tool options |
| Square Drive (Robertson) | CSA B18 | Very Low | Moderate–High | Square driver R1–R3 | None | Canadian EPC, electrical, HVAC |
| Hex Flange (Hex Washer) | ASME B18.6.3 | None | Highest | Hex wrench / socket | None | Where max torque + bearing area required |
1.4 — Load Characteristics and Failure Modes
Thread Stripping (Internal)
The most common machine screw failure mode in thin or soft tapped holes (aluminium, plastic, thin steel sheet). Thread strip-out force depends on: engaged thread length, material hardness, thread form, and minor diameter. Minimum engaged thread length for full strength = 1.0×d (steel into steel), 1.5×d (steel into aluminium), 2.0×d (steel into plastic).
Screw Body Fracture
Tensile fracture through the screw shank or thread root when applied torque generates axial load exceeding material UTS × stress area. More common with high-strength grades (12.9) in hard tapped holes where thread engagement is adequate. Prevention: calibrated torque wrench; do not exceed manufacturer’s proof torque recommendation.
Drive Recess Damage (Cam-Out)
Slotted and Phillips drives are designed to cam out at a specific torque level — a feature in production assembly (clutch effect) but destructive in maintenance environments where the screw must be removed and reused. In power-tool assembly, Torx or hex socket drives must be specified to prevent cam-out damage and stripped recesses.
Vibration Loosening
Machine screws in vibrating assemblies (rotating equipment panels, compressor enclosures, pump junction boxes) are susceptible to progressive nut-rotation loosening per the Junker effect. Prevention: prevailing-torque nuts (Nyloc), thread-locking adhesive (Loctite 243 for standard, 270 for permanent), spring washers (DIN 127), or serrated flange head screws with self-locking geometry.
Galvanic Corrosion
Stainless steel machine screws (A2 or A4) installed into aluminium housings create a galvanic couple in marine or humid environments. Insert isolation sleeves or use compatible metals (aluminium screws into aluminium, or anodised aluminium with SS isolation washers). Galvanic compatibility must be assessed using the galvanic series for the specific electrolyte and temperature.
Hydrogen Embrittlement (Grade 12.9)
Grade 12.9 machine screws (hardness 380–435 HV) are susceptible to hydrogen embrittlement from electroplating processes. Post-plate baking at 190°C for 4 hours minimum per ASTM F1941 is mandatory. Delayed fracture under sustained load occurs 12–72 hours after installation. For Grade 12.9 screws, specify Geomet, Dacromet, or PTFE coating instead of zinc electroplating.
1.5 — Preload and Torque Principles
T = Applied tightening torque (Nm)
K = Nut factor / torque coefficient:
K = 0.20 (dry, zinc-plated or plain)
K = 0.15 (light machine oil)
K = 0.13 (Loctite / thread adhesive)
K = 0.10 (PTFE tape / PTFE coat)
d = Nominal thread diameter (m)
Thread stripping check (tapped hole):
L_e(min) = 2 × F_c / (0.577 × π × d × τ_yield)
L_e = minimum thread engagement length (mm); τ_yield = shear yield strength of tapped material
A_s = 20.1 mm², S_p (8.8) = 580 MPa, Proof Load = 20.1 × 580 = 11,658 N
Target F_c = 0.70 × 11,658 = 8,161 N
Required torque T = 8,161 × 0.15 × 0.006 = 7.3 Nm
Minimum engagement in steel (τ_y = 0.577 × 640 = 369 MPa):
L_e = 2 × 8,161 / (π × 6 × 369) = 2.34 mm → specify min 6.0 mm (1.0×d)
1.6 — Design Safety Factors by Application
| Application Category | Safety Factor (UTS / Working Load) | Target Preload | Anti-Loosening Requirement | Engineering Note |
|---|---|---|---|---|
| Instrument panel / enclosure | 4:1 | 30–50% proof load | Not typically required | Controlled torque wrench; avoid over-torquing plastic |
| Electrical terminal / junction box | 4:1 | 40–60% proof load | Nyloc or thread lock recommended | Torque specification per terminal manufacturer |
| Valve actuator / body covers | 4:1 | 50–70% proof load | Required — vibration service | Hex socket or Torx drive; periodic inspection |
| Rotating equipment panels | 4:1–5:1 | 60–70% proof load | Mandatory — Nyloc, Loctite, or lockwasher | Vibration analysis; inspect per maintenance schedule |
| Precision instrument mounting | 5:1 | 30–40% proof load | Thread lock on request | Torque wrench mandatory; do not impact-drive |
| Pressure-retaining cover (small bore) | 4:1 | 60–70% proof load | Required — lockwasher or serrated flange | Grade 8.8 minimum; verify thread engagement |
| ATEX enclosure (Ex d / Ex e) | 5:1 | Per Ex manufacturer spec | Mandatory — per IEC 60079 Ex standard | Specific torque values in Ex enclosure certificate |
| Cryogenic / high-temp service | 4:1 | 50–65% proof load | Thread lock for cryogenic; spring washer for high-temp | Grade and material matched to temperature range |
Submit your BOM, head type, drive, grade, thread, coating, and quantity for a documented RFQ within 24 hours.
Thread Systems
& Standards Compliance
Machine screw dimensions — head diameter, head height, drive recess depth and width, thread diameter, pitch, and length — are precisely defined by ASME B18.6.3 (inch), ISO 1207 / 7045 / 14583 (metric), and DIN 84 / 963 / 965 / 7985 (metric). All applicable standards are supported at RR Hydraulic with full certification capability.
Submit head type, drive, grade, thread, material, coating, and quantity to sales@rrhydraulics.com for a fully certified commercial offer.
2.1 — ISO Metric Machine Screw Dimensional Table
The following table provides key dimensional data for the most common metric machine screw head types — pan head (ISO 7045 / DIN 7985) and countersunk head (ISO 7046 / DIN 965) — in metric coarse thread. Thread tolerance 6g (bolt) per ISO 965.
| Thread | Pitch (mm) | Stress Area (mm²) | Pan Head Dia (mm) | Pan Head Height (mm) | CSK Head Dia (mm) | CSK Head Height (mm) | Cheese Head Dia (mm) | Standard Length Range (mm) |
|---|---|---|---|---|---|---|---|---|
| M1.6 | 0.35 | 1.27 | 3.2 | 1.30 | 3.0 | 0.96 | 3.0 | 2 – 16 |
| M2 | 0.40 | 2.07 | 4.0 | 1.60 | 3.8 | 1.20 | 3.8 | 3 – 20 |
| M2.5 | 0.45 | 3.39 | 5.0 | 2.00 | 4.7 | 1.50 | 4.5 | 4 – 25 |
| M3 | 0.50 | 5.03 | 6.0 | 2.40 | 5.6 | 1.65 | 5.5 | 5 – 50 |
| M3.5 | 0.60 | 6.78 | 7.0 | 2.80 | 6.5 | 1.93 | 6.0 | 6 – 50 |
| M4 | 0.70 | 8.78 | 8.0 | 3.10 | 7.5 | 2.20 | 7.0 | 6 – 80 |
| M5 | 0.80 | 14.2 | 9.5 | 3.65 | 9.2 | 2.50 | 8.5 | 8 – 100 |
| M6 | 1.00 | 20.1 | 12.0 | 4.65 | 11.0 | 3.00 | 10.0 | 10 – 120 |
| M8 | 1.25 | 36.6 | 16.0 | 6.00 | 15.0 | 4.00 | 13.0 | 12 – 160 |
| M10 | 1.50 | 58.0 | 20.0 | 7.50 | 18.3 | 5.00 | 16.0 | 16 – 200 |
| M12 | 1.75 | 84.3 | 24.0 | 8.50 | 22.0 | 6.00 | 18.0 | 20 – 200 |
2.2 — ASME B18.6.3 Inch Series Machine Screw Dimensional Table
Inch-series machine screws per ASME B18.6.3 are designated by number (#0 through #12) for sizes below ¼” and by fractional inch for ¼” and above. Thread: UNC (coarse) or UNF (fine) per ASME B1.1. Pan head and flat (countersunk) head are the most common types.
| Size | Decimal Dia (in) | TPI (UNC) | TPI (UNF) | Stress Area UNC (in²) | Pan Head Dia (in) | Pan Head Ht (in) | Flat Head Dia (in) | Length Range (in) |
|---|---|---|---|---|---|---|---|---|
| #0 | 0.0600 | — | 80 | 0.00180 | 0.116 | 0.039 | 0.119 | ⅛ – ¾ |
| #1 | 0.0730 | 64 | 72 | 0.00263 | 0.142 | 0.046 | 0.146 | ⅛ – 1 |
| #2 | 0.0860 | 56 | 64 | 0.00370 | 0.167 | 0.053 | 0.172 | ⅛ – 1 |
| #3 | 0.0990 | 48 | 56 | 0.00487 | 0.193 | 0.060 | 0.199 | ⅛ – 1½ |
| #4 | 0.1120 | 40 | 48 | 0.00604 | 0.219 | 0.068 | 0.225 | ¼ – 2 |
| #6 | 0.1380 | 32 | 40 | 0.00909 | 0.270 | 0.082 | 0.279 | ¼ – 2 |
| #8 | 0.1640 | 32 | 36 | 0.01400 | 0.322 | 0.096 | 0.332 | ¼ – 3 |
| #10 | 0.1900 | 24 | 32 | 0.01750 | 0.373 | 0.110 | 0.385 | ¼ – 3 |
| #12 | 0.2160 | 24 | 28 | 0.02420 | 0.425 | 0.125 | 0.438 | ¼ – 3 |
| ¼” | 0.2500 | 20 | 28 | 0.03180 | 0.492 | 0.144 | 0.507 | ¼ – 4 |
| 5/16″ | 0.3125 | 18 | 24 | 0.05240 | 0.615 | 0.178 | 0.635 | ¼ – 4 |
| ⅜” | 0.3750 | 16 | 24 | 0.07750 | 0.740 | 0.212 | 0.762 | ⅜ – 4 |
2.3 — Applicable Standards and Compliance Framework
ASME B18.6.3
Machine screws, tapping screws, and metallic drive screws — inch series. The primary dimensional and material standard for inch machine screws in North American and ASME-coded EPC projects. Defines all head types (pan, flat, oval, fillister, binding, truss), drive recesses, thread class (2A, UNC/UNF), and material requirements.
ISO 1207
Slotted cheese head screws — product grade A, metric coarse. The European equivalent of the cheese head machine screw. Dimensional data and material property class per ISO 898-1. Widely used in European EPC instrumentation and control panel assemblies where cheese head geometry provides maximum bearing area.
ISO 7045
Pan head screws with type H or type Z cross recesses — metric, product grade A. The most commonly specified metric machine screw in European EPC, industrial, and electronic assembly. Phillips (H) and Pozidriv (Z) drive recesses defined. Material: property class 4.8 standard; 8.8 / 10.9 available for high-strength applications.
ISO 14583
Hexalobular (Torx) socket pan head screws — metric. Defines the Torx drive recess (TX designation) with 6-lobed star geometry. Superior torque transmission, no cam-out, and high drive bit engagement make this the preferred drive for precision and high-torque machine screw applications. Property class 8.8 and 10.9 standard.
DIN 84 / DIN 963 / DIN 965
DIN 84: slotted cheese head screws. DIN 963: slotted countersunk flat head screws. DIN 965: cross-recessed countersunk flat head screws. These legacy DIN standards are still widely specified in European plant replacement supply and German EPC equipment documentation. Dimensionally aligned with ISO equivalents but with minor tolerance differences in some sizes.
ISO 898-1
Mechanical properties of fasteners — bolts, screws, and studs; metric series. Property classes 4.6, 4.8, 5.8, 8.8, 10.9, 12.9 define UTS, proof/yield strength, elongation, and hardness for metric machine screws. Class 4.8 is the standard for general machine screw supply; 8.8 for structural / high-clamping applications; 12.9 for maximum strength.
ISO 3506
Mechanical and physical properties of corrosion-resistant stainless steel fasteners. Parts 1–3 cover bolts/screws, nuts, and set screws. Property class designations: A2-70 (SS 304, 700 MPa UTS), A2-80 (strain-hardened SS 304), A4-70 (SS 316), A4-80 (strain-hardened SS 316). The governing standard for SS machine screws in marine, offshore, and chemical service.
ASTM F837 / F879
ASTM F837: Stainless steel socket head cap screws — inch series. ASTM F879: Stainless steel socket button and flat head cap screws. These standards govern the mechanical properties, dimensional requirements, and corrosion resistance testing for SS machine screws in US-coded projects. Material: 18-8 (SS 304) or 316 SS.
NACE MR0175 / ISO 15156
Materials for H₂S sour environments. Carbon steel machine screws in sour service: max hardness 22 HRC — limits practical maximum strength to approximately ISO Grade 8.8. Grade 10.9 and 12.9 carbon steel machine screws exceed the NACE hardness limit and are NOT acceptable in sour service without specific engineering approval. SS A4-70 / A4-80 are NACE-compliant alternatives.
2.4 — Thread Form and Compatibility Reference
| Thread System | Standard | Size Range | Pitch / TPI | Tolerance Class (Screw/Hole) | Regional Standard | Interchangeability Note |
|---|---|---|---|---|---|---|
| UNC Coarse | ASME B1.1 | #1–¾” | 16–64 TPI | 2A / 2B | ASME B18.6.3 | Standard US / Canadian EPC; not interchangeable with metric |
| UNF Fine | ASME B1.1 | #0–¾” | 24–80 TPI | 2A / 2B | ASME B18.6.3 | Precision / thin-wall; not interchangeable with UNC |
| Metric Coarse (ISO) | ISO 261 / DIN 13 | M1.6–M12 | 0.35–1.75 mm | 6g / 6H (std); 4g/5H (precision) | ISO 1207 / 7045 / 14583 | Standard European / Asian EPC |
| Metric Fine (ISO) | ISO 261 | M3–M12 | 0.5–1.25 mm | 6g / 6H | Special order | Thin-wall, vibration; not interchangeable with coarse |
| BSW (Whitworth) | BS 84 | ⅛”–¼” | 20–40 TPI | Class 1–2 | Legacy BS 450 / BS 1981 | Legacy UK plant; not interchangeable with UNC |
| BA (British Association) | BS 57 | 0BA–16BA | Fine | BS 57 | BS 450 | Legacy electrical / instrument; replacement procurement only |
2.5 — Torque Chart: Machine Screw Installation
The following table provides recommended installation torque values for metric machine screws at ISO property classes 4.8, 8.8, and 10.9, and for SS grades A2-70 and A4-80. Values target 70% of proof load — the standard initial preload target for machine screw assemblies unless otherwise specified by the equipment manufacturer.
| Thread | Class 4.8 Torque Nm (dry) | Class 8.8 Torque Nm (dry) | Class 10.9 Torque Nm (dry) | Class 12.9 Torque Nm (dry) | A2-70 Torque Nm (dry) | A4-80 Torque Nm (dry) | Lubricated Factor |
|---|---|---|---|---|---|---|---|
| M2 | 0.2 | 0.4 | 0.5 | 0.6 | 0.3 | 0.4 | ×0.75 |
| M2.5 | 0.4 | 0.7 | 0.9 | 1.1 | 0.6 | 0.7 | ×0.75 |
| M3 | 0.8 | 1.4 | 1.7 | 2.0 | 1.1 | 1.3 | ×0.75 |
| M3.5 | 1.2 | 2.2 | 2.6 | 3.1 | 1.7 | 2.0 | ×0.75 |
| M4 | 1.8 | 3.2 | 3.9 | 4.6 | 2.5 | 2.9 | ×0.75 |
| M5 | 3.5 | 6.3 | 7.6 | 9.0 | 5.0 | 5.8 | ×0.75 |
| M6 | 6.1 | 10.9 | 13.2 | 15.5 | 8.7 | 10.2 | ×0.75 |
| M8 | 15.0 | 26.0 | 31.5 | 37.0 | 20.8 | 24.3 | ×0.75 |
| M10 | 29.0 | 52.0 | 63.0 | 74.0 | 41.5 | 48.5 | ×0.75 |
| M12 | 50.0 | 90.0 | 110.0 | 128.0 | 72.0 | 84.0 | ×0.75 |
| #6 UNC | 0.7 | 1.4 | — | — | 1.0 | 1.2 | ×0.75 |
| #10 UNC | 1.4 | 2.8 | — | — | 2.0 | 2.4 | ×0.75 |
| ¼” UNC | 3.2 | 6.1 | 7.4 | 8.7 | 4.8 | 5.6 | ×0.75 |
| ⅜” UNC | 10.5 | 19.8 | 24.0 | 28.2 | 15.8 | 18.5 | ×0.75 |
Property Classes
& Manufacturing Process
Machine screw material selection spans the widest range of any fastener category — from low-carbon steel (Class 4.8) for general panel assembly to Grade 12.9 alloy steel for precision high-strength applications, and from SS A2-70 for standard corrosive service to Inconel and titanium for extreme environments. RR Hydraulic manufactures machine screws in all grades and materials with full EN 10204 traceability.
3.1 — Material Grade Overview and Mechanical Properties
| Grade / Class | Spec | Base Material | UTS (MPa) | Proof Strength (MPa) | Temp Range (°C) | HRC Max | Primary Application |
|---|---|---|---|---|---|---|---|
| Class 4.8 | ISO 898-1 | Low/med carbon steel | 420 | 340 | −20 to +300 | — | General panel, enclosure, sheet metal assembly |
| Class 5.8 | ISO 898-1 | Medium carbon steel | 520 | 415 | −20 to +300 | — | Medium-load instrument assembly |
| Class 8.8 | ISO 898-1 | Med-carbon alloy Q&T | 800 | 640 | −20 to +300 | 34 | Structural, valve covers, machinery assembly |
| Class 10.9 | ISO 898-1 | Alloy steel Q&T | 1040 | 940 | −20 to +300 | 39 | High-strength precision mechanical assembly |
| Class 12.9 | ISO 898-1 | Alloy steel Q&T | 1220 | 1100 | −20 to +300 | 44 | Maximum strength; no HDG; H₂E risk if electroplated |
| A2-70 | ISO 3506 | SS 304 | 700 | 450 | −196 to +300 | — | Corrosive, food, pharma, mild chemical |
| A2-80 | ISO 3506 | SS 304 strain-hardened | 800 | 640 | −196 to +300 | — | Higher-strength SS applications |
| A4-70 | ISO 3506 | SS 316 | 700 | 450 | −196 to +300 | — | Marine, offshore, chloride, NACE service |
| A4-80 | ISO 3506 | SS 316 strain-hardened | 800 | 640 | −196 to +300 | — | High-strength marine / offshore; NACE compliant |
| Duplex 2205 | UNS S31803 | Duplex SS | 620 | 450 | −50 to +315 | 28 | Offshore, subsea, sour + chloride combined |
| Titanium Gr.5 | ASTM F835 | Ti-6Al-4V | 900 | 830 | −200 to +315 | — | Aerospace, weight-critical, cryogenic |
| Brass (Cu-Zn) | ISO 8839 | CuZn37 | 380 | — | −200 to +150 | — | Non-magnetic, electrical, non-sparking |
| Nylon (PA66) | ISO 7049 / DIN 7985 | Polyamide 66 | — | — | −40 to +120 | — | Electrical isolation, non-magnetic, lightweight |
3.2 — Mechanical Properties by Grade
| Grade / Class | UTS (MPa) | Proof Strength (MPa) | Elongation (%) | Hardness Min (HV) | Hardness Max (HV) | Core Hardness (HRC) | NACE MR0175 Compliant? |
|---|---|---|---|---|---|---|---|
| 4.8 | 420 | 340 | 14 | 130 | 250 | — | Yes |
| 5.8 | 520 | 415 | 10 | 155 | 280 | — | Yes |
| 8.8 (d≤16mm) | 800 | 640 | 12 | 245 | 320 | Max 34 | Yes (HRC check req.) |
| 10.9 | 1040 | 940 | 9 | 300 | 380 | Max 39 | No — exceeds 22 HRC |
| 12.9 | 1220 | 1100 | 8 | 385 | 435 | Max 44 | No — exceeds 22 HRC |
| A2-70 | 700 | 450 | 20 | — | Max 250 HV | — | Yes |
| A2-80 | 800 | 640 | 8 | — | Max 320 HV | — | Yes |
| A4-70 | 700 | 450 | 20 | — | Max 250 HV | — | Yes |
| A4-80 | 800 | 640 | 8 | — | Max 320 HV | — | Yes |
| Duplex 2205 | 620 | 450 | 25 | — | Max 293 HB | Max 28 | Yes (28 HRC max) |
3.3 — Corrosion Resistance by Material vs Service Environment
| Material | Marine / Offshore Atmos. | H₂S / Sour* | Cl⁻ / Seawater | Acids (HCl / H₂SO₄) | Alkaline / Caustic | High Temp (>200°C) | Non-Magnetic |
|---|---|---|---|---|---|---|---|
| Class 4.8 / 8.8 CS (zinc plated) | Fair | Conditional* | Poor | Poor | Good | Good to 300°C | No |
| Class 8.8 CS (HDG) | Good | Conditional* | Fair | Poor | Good | Good to 200°C | No |
| A2-70 (SS 304) | Good | Fair | Poor (SCC risk) | Fair | Very Good | Good to 300°C | Slightly mag. |
| A4-70 (SS 316) | Very Good | Good | Fair | Good | Very Good | Good to 300°C | Slightly mag. |
| A4-80 (SS 316 SH) | Very Good | Good | Fair | Good | Very Good | Good to 300°C | Slightly mag. |
| Duplex 2205 | Excellent | Very Good | Very Good | Very Good | Very Good | Limited >315°C | Slightly mag. |
| Titanium Gr.5 | Excellent | Excellent | Excellent | Excellent | Excellent | Limited >315°C | Yes |
| Brass (CuZn37) | Fair | Poor (SCC) | Fair | Poor | Fair | Limited >150°C | Yes |
| Nylon PA66 | Excellent | Excellent | Excellent | Good | Good | Max 120°C | Yes |
* Sour service: Carbon steel Classes 10.9 and 12.9 NOT acceptable (exceed 22 HRC per NACE MR0175). Use Class 8.8 (verify hardness) or SS A4-70 / A4-80 for sour-adjacent enclosures and instrument panels.
3.4 — Manufacturing Process
3.4.1 — Cold Heading (Cold Forming)
Machine screws are manufactured primarily by cold heading — a cold-forging process that forms the head and drive recess from wire stock in a multi-station die set without material removal. Cold heading produces continuous grain flow through the head, producing superior fatigue resistance and mechanical strength compared to machined heads. The drive recess (Phillips, Torx, hex socket) is formed simultaneously with the head in the final die stage, ensuring precise recess geometry and consistent drive engagement across all production units.
3.4.2 — Thread Rolling
Machine screw threads are formed by thread rolling — cold-forming the thread profile by compressing the wire blank between rotating dies. Thread rolling produces compressive residual stress at the thread root, continuous grain flow through the thread form, superior surface finish (Ra ≤ 0.8 µm at thread root), and higher fatigue life compared to cut threads. Thread dimensional accuracy is governed by ISO 965 (metric, 6g class) or ASME B1.1 (UNC/UNF, Class 2A).
3.4.3 — Drive Recess Dimensional Requirements
- Slotted drive: Slot width and depth per ISO 2009 / ASME B18.6.3 — minimum slot depth determines maximum driver blade engagement and torque capacity
- Phillips / Pozidriv: Drive recess number (#0–#4) matches screw size per manufacturer’s recommendation table; recess depth and cam-out geometry per ISO 4757 / ASME B18.6.3
- Torx (TX): Drive size T6–T40 for M2–M12; 6-lobe geometry per ISO 14583; inscribed circle diameter within ±0.01 mm tolerance for consistent bit engagement
- Hex socket: Socket size across flats per ISO 4762; socket depth minimum 1.5× nominal across flats; concentricity to shank axis within 0.1 mm TIR
- Common rule: Drive recess depth must not penetrate into the threaded shank — minimum distance from recess bottom to thread start per applicable standard
3.5 — Surface Finish and Coating Options
| Finish | Specification | Thickness (µm) | Salt Spray (h) | H₂E Risk (Gr. 12.9)? | Drive Recess Impact | Typical Application |
|---|---|---|---|---|---|---|
| Plain / Bare | As-manufactured | — | <24 | None | None | Internal dry assembly; immediate assembly |
| Black Oxide | MIL-DTL-13924 | 1–2 | 24–72 | Low | None | Indoor mechanical assembly, optical instruments |
| Zinc Electroplate | ASTM B633 / ISO 4042 | 5–25 | 96–500 | HIGH for Gr. 12.9 | Slight thickening — check recess fit | General EPC, panel, enclosure assembly |
| Yellow Zinc / Chromate | ASTM B633 Type III | 5–25 + chromate | 200–500 | HIGH for Gr. 12.9 | Slight — check recess and thread fit | Enhanced corrosion protection; standard CS screws |
| Geomet / Dacromet | ISO 10683 | 8–12 | 1000–1500 | None | Minimal | Outdoor, marine-adjacent; no thread oversize needed |
| Nickel Plate | ASTM B689 | 5–25 | 200–500 | Moderate | Slight | Decorative, non-magnetic instrument panels |
| PTFE Coat | Proprietary | 20–50 | 1000+ | None | Minimal — check drive recess fit | Precision torque; chemical resistance; SS anti-galling |
| Passivation (SS only) | ASTM A380 / A967 | Passive layer | 500–2000+ | None | None | Standard finish on all SS machine screws |
| Anodising (Aluminium only) | ISO 7599 / MIL-A-8625 | 5–25 | 1000+ | None | None (pre-coating) | Aluminium machine screws in aerospace / weight-critical |
Industry Applications
& Documentation
RR Hydraulic maintains full traceability from raw wire stock to final packed shipment on all machine screw orders. Dimensional inspection reports, EN 10204 3.1 / 3.2 MTRs, drive recess gauging reports, coating certificates, hardness test results, and complete EPC export documentation packages are provided as standard on all project-grade supply.
4.1 — Inspection & QC Protocol
4.2 — EN 10204 Material Test Certificate Requirements
| Certificate | Content | Signatory | Standard EPC Requirement | When Mandatory for Machine Screws |
|---|---|---|---|---|
| 2.1 | Conformity declaration only | Manufacturer | General commercial supply | Non-critical general assembly; hardware store equivalent |
| 2.2 | Non-specific test results | Manufacturer | Standard EPC panel / enclosure supply | General EPC instrument and enclosure assembly |
| 3.1 | Heat-traceable mech + chem; specific to production lot | Manufacturer’s authorised QC Inspector | EPC O&G, instrument, pressure-retaining cover | All NACE service, Grade 8.8+ structural, Ex enclosures |
| 3.2 | 3.1 + countersigned by TPI | Manufacturer + SGS / BV / DNV | Critical: NACE, nuclear, offshore instrument | Sour service, offshore ATEX, nuclear Class 2/3 |
4.3 — Applications by Industry
Instrumentation & Control Panels — EPC
Machine screws (M3–M6, Class 4.8 or 8.8, zinc-plated or A4-70 for marine/offshore) are the primary fasteners in DCS/PLC panels, instrument racks, marshalling cabinets, and terminal blocks. Torque specifications per panel manufacturer’s documentation. A4-70 SS mandatory for offshore and coastal facilities. EN 10204 2.2 standard; 3.1 for O&G offshore projects.
ATEX / Ex Enclosures — Oil & Gas
Machine screws in Ex d (flameproof) and Ex e (increased safety) enclosures are safety-critical — specified in the enclosure’s Ex certificate with mandatory torque values. Grade 8.8 or A4-70 SS as specified by the Ex enclosure manufacturer. Torque must be applied with a calibrated torque screwdriver and recorded in the installation documentation. Non-compliance voids Ex certification.
Valve Actuators & Positioners
Machine screws secure actuator covers, positioner housings, limit switch brackets, and solenoid valve bodies on control valves. A4-70 SS for outdoor and process environments; Grade 8.8 for high-torque cover applications. Vibration service requires Nyloc nuts or Loctite 243 thread lock. Torx or hex socket drives specified to prevent cam-out during field service.
Offshore Platform Electronics
All machine screws in offshore electronics, instrument enclosures, and junction boxes in marine atmosphere must be minimum A4-70 SS — carbon steel with any coating degrades rapidly in offshore chloride-laden atmosphere, causing galvanic corrosion with aluminium housings. Duplex 2205 screws specified in splash zone and continuously wet environments. EN 10204 3.1 minimum.
Precision Machinery Assembly
Grade 10.9 or 12.9 machine screws (M3–M10) in socket head cap screw (SHCS) configuration are used in precision mechanical assemblies: bearing housings, gear covers, actuator bodies, and servo motor mounting. Torx or hex socket drives. PTFE or Geomet coating for Grade 12.9 — electroplating prohibited without confirmed ASTM F1941 bake-out. Calibrated torque wrench mandatory.
Food & Pharmaceutical — Hygienic Applications
A4-70 or A4-80 SS machine screws with smooth pan or countersunk heads in all process-contact zone enclosures, inspection covers, and equipment panels. No Phillips drive — food-grade facilities prefer Torx or hex socket for positive drive without debris accumulation in recess. Passivated finish per ASTM A967. Full material traceability per EU 10/2011 or 21 CFR for direct food-contact parts.
4.4 — Export Packaging Specification
- Machine screws bulk-packed in polybags or individual compartment trays per head type, thread, length, grade, and coating — prevents mixing and enables direct BOM picking at project site without re-sorting
- Anti-static packaging for machine screws destined for electronic / instrument assembly environments — prevents electrostatic discharge damage to sensitive components during co-packaging
- VCI (Volatile Corrosion Inhibitor) poly bag packaging for all plain, black oxide, and zinc-plated carbon steel machine screws — prevents atmospheric oxidation during ocean freight and extended site storage up to 18 months
- Lot tagging: each polybag labelled with thread size, length, head type, drive type, property class/grade, material, surface finish, heat/lot number, quantity, and PO item reference — full traceability through shipping chain
- Compartmented carton or tray packaging available for multi-size BOM kits — eliminates mis-picking errors in large instrument panel assembly kits shipped to site
- Outer crating: ISPM-15 heat-treated wooden crates for all international export; inner cartons labelled per UN packaging regulations for coated fastener classification
- Documentation package: packing list, EN 10204 MTC, coating certificate, and FAI report enclosed with each lot shipment — cross-referenced to lot number on each polybag label
4.5 — Complete EPC Project Documentation Package
| # | Document | Standard / Format | Mandatory / Conditional | Notes |
|---|---|---|---|---|
| 01 | Material Test Certificate (MTC) | EN 10204 2.2 / 3.1 / 3.2 | Mandatory — grade per project spec | Heat/wire lot traceable |
| 02 | Chemical Composition Report | Wire / bar stock lot certified lab | Mandatory — 3.1 / 3.2 orders | Per ISO 898-1 / ISO 3506 chemistry limits |
| 03 | Mechanical Properties Report | UTS, proof strength, hardness | Mandatory — 3.1 / 3.2 orders | Proof load test + hardness per grade |
| 04 | Hardness Test Report | ISO 6507 Vickers / ASTM E18 Rockwell | Mandatory — Grade 8.8+ and NACE | Core hardness per lot; HRC conversion reported |
| 05 | Dimensional Inspection Report | Per ISO /DIN/ ASME B18.6.3 | Mandatory | Thread gauge, head, drive recess, length |
| 06 | Drive Recess Gauge Report | Per ISO 4757 / ISO 10664 / ASME B18.6.3 | Mandatory — EPC instrument / Ex supply | Drive size and depth per applicable standard |
| 07 | Proof Load Test Report | ISO 898-1 Annex / ASTM F606 | Conditional — Grade 8.8+ structural | No permanent set at proof load |
| 08 | Drive Torque-to-Failure Report | ISO 898-1 Annex | Conditional — Ex enclosure, precision | Failure in shank, not drive recess |
| 09 | Surface Finish / Coating Certificate | ISO 4042 / ISO 10683 / ASTM B633 | Mandatory — all coated supply | Thickness + salt spray hours per lot |
| 10 | Hydrogen Bake-Out Certificate | ASTM F1941 | Mandatory — Grade 12.9 electroplated | 190°C × 4h; dated; batch-specific |
| 11 | PMI Report (XRF) | Per lot — SS / duplex / exotic grades | Mandatory — non-CS grades | A2 (304) vs A4 (316) differentiation |
| 12 | First Article Inspection (FAI) Report | Project-specific format | Mandatory — new configs / first lots | Released before batch production |
| 13 | TPI Witness Certificate | SGS / BV / DNV / Lloyds | Conditional — EN 10204 3.2 / ATEX / nuclear | Co-witness at manufacturer works |
| 14 | NACE Compliance Statement | Hardness + grade confirmation | Conditional — sour service supply | Grade 8.8 hardness ≤320 HV verified |
| 15 | ATEX / Ex Enclosure Torque Record | Per IEC 60079 Ex certificate | Conditional — Ex enclosure supply | Specific torque values from Ex cert attached |
| 16 | ISO 9001:2015 Certificate | Third-party QMS certification | Mandatory — EPC projects | Scope covering machine screw manufacture |
| 17 | Country of Origin Certificate | Chamber of Commerce | Mandatory — all export | HS code for customs classification |
| 18 | Packing List | Item-level per shipment | Mandatory | Cross-references lot numbers and MTC |
| 19 | Commercial Invoice | Per INCOTERMS 2020 | Mandatory | Includes HS tariff code |
| 20 | Bill of Lading / Air Waybill | Per freight mode | Mandatory | Issued by freight forwarder |
4.6 — ISO and Quality System Compliance
ISO 9001:2015
Quality Management System covering wire stock supplier qualification, cold heading process control, thread rolling dimensional verification, drive recess gauging, heat treatment control, coating process qualification, hardness testing, and final inspection release. Mandatory for EPC, O&G, and instrumentation project procurement qualification. RR Hydraulic holds current ISO 9001:2015 certification.
ISO 10474
Steel and steel products — inspection documents. Source framework for EN 10204 certificate types. Some EPC project specifications for instrumentation and panel assembly reference ISO 10474 Type 2.2 or 3.1.B — these map to EN 10204 2.2 and 3.1 respectively. RR Hydraulic can provide documentation in either format on request.
IEC 60079 (ATEX)
Explosive atmospheres — equipment protection. Machine screws in Ex d (IEC 60079-1) and Ex e (IEC 60079-7) enclosures are safety-critical components. The Ex enclosure certificate specifies the screw grade, size, and mandatory torque value. Non-standard screws or incorrect torque invalidate the Ex certificate — supply of Ex enclosure machine screws requires reference to the specific Ex certificate number.
ISO 4413
Safety requirements for hydraulic fluid power systems. Machine screws used in hydraulic valve body covers, HPU inspection covers, and hydraulic manifold port plugs must be rated for the system design pressure and comply with ISO 4413 cleanliness requirements. Bore and thread cleanliness post-manufacturing: ISO 4406 code 16/13 or better for hydraulic system machine screw applications.
Submit your BOM, head type, drive system, grade, material, coating, and quantity to RR Hydraulic for a complete, certified commercial offer.