RFQ Today
Certifications available: EN 10204 3.1 / 3.2 MTRs, ISO 3506 SS grades, NACE MR0175 compliance, Third-Party Inspection, ASTM / DIN / ISO / BS standards, and complete EPC export documentation packages.
Self-Tapping Screws
A world-class technical reference for EPC contractors, mechanical and structural engineers, procurement heads, TPI inspection agencies, and global project buyers specifying self-tapping screws in sheet metal fabrication, enclosure assembly, cable management, HVAC, roofing, cladding, and industrial construction across Oil & Gas, Power Generation, Petrochemical, and Infrastructure sectors.
Thread-Forming Types
& Load Characteristics
Self-tapping screws are fasteners that create their own mating thread as they are driven into a pre-drilled pilot hole — or in some cases directly into the substrate without any pre-drilling. They eliminate the need for a separately tapped hole, dramatically reducing assembly time and tooling cost in thin sheet metal, plastic, light alloy, timber, and composite material assembly across EPC construction, equipment enclosures, and industrial fabrication projects.
1.1 — Technical Definition and Functional Role
A self-tapping screw is defined by its ability to form or cut a mating thread in the receiving material during installation, without the need for a pre-tapped hole. The thread is formed either by cutting (removing material) in thread-cutting types, or by displacing and cold-forming the substrate material (thread-forming / thread-rolling types) for ductile metals and plastics. The critical difference between these two mechanisms determines the pull-out strength, the suitability for different substrate materials, and the reusability of the joint.
In EPC and industrial environments, self-tapping screws are the primary fastener in: electrical enclosure sheet metal panels, cable tray and trunking assembly, HVAC ductwork and cladding, instrument shelter roof and wall panels, modular building steel frame cladding, equipment platform grating clips, junction box and marshalling cabinet fabrication, pipe insulation cladding band fastening, and light structural steel connection of secondary members. Their selection — covering thread type, head profile, drive system, point type, material grade, and coating — directly determines joint integrity, pull-out strength, corrosion life, and re-entry capability.
RR Hydraulic manufactures and exports self-tapping screws to global EPC projects under all applicable international standards with EN 10204 3.1 / 3.2 material traceability and complete project documentation.
1.2 — Self-Tapping Screw Classification: Thread Types
Thread-Cutting Type A (Spaced Thread)
Coarse thread with tapered point. Designed for sheet metal and light gauge steel. Thread pitch is coarser than Type B — reduced driving torque with good pull-out in thin materials. Per ASME B18.6.4 Type A / ISO 1481 / DIN 7971. Requires a pre-drilled pilot hole sized to the material thickness and thread diameter table.
Thread-Cutting Type B (Blunt Point)
Finer thread than Type A, with a blunt tapered point. Designed for heavier gauge sheet metal, non-ferrous castings, and plastics. More thread engagement per unit length — higher pull-out strength than Type A in thicker materials. Per ASME B18.6.4 Type B / ISO 1482 / DIN 7972. Standard for most industrial metal enclosure and panel assembly.
Thread-Cutting Type BT (Trilobe / Thread-Forming)
Triangular cross-section shank with rolled (not cut) thread — displaces and work-hardens the mating material rather than cutting it. Produces no swarf, creates a tighter thread engagement, and generates a stronger joint in ductile metal. Preferred for aluminium, brass, and ductile steel assemblies. Excellent reusability — thread form is preserved on removal.
Thread-Cutting Type C
Machine-screw thread form (similar pitch to UNC) with a cutting notch at the point. Used where a machine-screw thread compatibility in the tapped hole is required — allowing a machine screw to replace the self-tapping screw on reassembly. Per ASME B18.6.4 Type C / ISO 1483 / DIN 7973. Common in electrical enclosure maintenance-access panels.
Self-Drilling (TEK) Screw
Combined drill point and thread-forming screw — the drill tip penetrates the substrate and the thread engages without pre-drilling. Class ratings 1–5 define the maximum steel thickness the drill tip can penetrate (Class 1: ≤1.6 mm; Class 5: ≤12.7 mm). Per DIN 7504 / EN ISO 15480. Used in structural cladding, steel framing, and decking attachment where pre-drilling is impractical.
Hi-Lo Thread Screw
Dual thread form: alternating high and low thread crests. The high thread engages the substrate; the low thread between each high thread provides additional material displacement resistance without increasing driving torque. Optimised for plastics and fibre-reinforced composites. Provides up to 30% higher pull-out strength than standard thread in plastic housings and GRP enclosures.
Sheet Metal Screw (SMS)
General designation for spaced-thread screws designed for thin sheet metal. Encompasses Type A, B, and AB thread forms. The SMS designation is commonly used in commercial and procurement contexts; the engineering specification must always reference the specific ISO / DIN / ASME B18.6.4 thread type for dimensional accuracy and pull-out strength prediction.
Concrete / Masonry Self-Tapping Screw
Hardened carbon steel or stainless steel screw with a special high-low thread form designed to anchor into pre-drilled concrete, masonry, or aerated concrete (Ytong) blocks. Eliminates the need for a separate anchor. Per ETAG 001 / ETA approval. Used in EPC for conduit saddle fixing, cable support, equipment base anchoring, and structural attachment to concrete walls and slabs.
1.3 — Thread Type vs Substrate Material: Engineering Selection
| Thread Type | Thin Steel (<1.5 mm) | Heavy Steel (1.5–6 mm) | Aluminium | Stainless Steel | Plastics / GRP | Timber / Composite | Concrete / Masonry | Pilot Hole Required? |
|---|---|---|---|---|---|---|---|---|
| Type A | Excellent | Fair | Good | Poor | Good | Good | No | Yes |
| Type B | Good | Excellent | Excellent | Fair | Good | Fair | No | Yes |
| Type BT (Trilobe) | Good | Excellent | Excellent | Good | Fair | No | No | Yes |
| Type C | Poor | Good | Good | Fair | Fair | No | No | Yes |
| Self-Drilling (TEK) | Excellent | Excellent (Class 3–5) | Good | Fair | No | No | No | No — self-drilling |
| Hi-Lo Thread | Fair | Fair | Good | Poor | Excellent | Good | No | Yes |
| Concrete Screw | No | No | No | No | No | No | Excellent | Yes (hammer drill) |
1.4 — Load Characteristics and Structural Behaviour
Pull-Out Strength (Axial)
The critical structural load mode for self-tapping screws in thin sheet metal and cladding. Pull-out strength depends on: screw thread outer diameter, thread pitch, engaged thread length (material thickness), substrate yield strength, and hole preparation accuracy. Pull-out strength prediction per ECCS Recommendations or Eurocode 3 Part 1-3 (cold-formed steel). Never substitute a smaller thread pitch or shorter screw without recalculating pull-out.
Shear (Bearing) Strength
Lateral load perpendicular to the screw axis. Governed by the bearing capacity of the thinner sheet at the screw shank — net section failure or bearing failure modes per Eurocode 3 Part 1-3. Shear capacity depends on screw diameter, material thickness, and screw spacing (edge distance and pitch). In cladding and roofing, design shear load from wind uplift governs fastener layout.
Torque-Tension Relationship
Unlike machine screws in tapped holes, self-tapping screws generate their own thread during installation — driving torque includes both thread-forming torque (creating the mating thread) and the tightening torque (generating clamp load). The driving torque must exceed the thread-forming torque but not exceed the screw’s torsional strip-out limit. Calibrated power tools with adjustable clutch are required for consistent installation.
Tilt and Pull-Through
Pull-through failure occurs when the screw head pulls through the sheet material under load — particularly in thin-gauge steel (≤1.0 mm) and aluminium cladding under wind uplift. Prevented by: using screws with a sealing washer (EPDM, neoprene, or metal bonded), ensuring correct head bearing area, and not over-torquing which crushes the washer and reduces bearing area.
Vibration Loosening
Self-tapping screws in vibrating assemblies (HVAC ductwork, equipment panels on rotating machinery, compressor enclosures) are susceptible to thread disengagement under cyclic transverse vibration (Junker effect). Thread-forming types (BT) retain engagement better than thread-cutting types. For vibration service, specify self-locking serrated washer heads, thread lock adhesive (Loctite 243), or mechanical locking washers.
Corrosion at Fastener Point
Self-drilling and self-tapping screws in roofing and external cladding are a primary site for corrosion initiation — the drill point or cutting tip disrupts the protective coating on both the screw and the substrate at the point of penetration. Screws with oversized EPDM bonded washers seal the penetration point. For coastal and marine environments, specify SS or Geomet-coated screws with EPDM washers matched to the substrate coating system.
1.5 — Pilot Hole Sizing: Critical Engineering Parameter
d_minor = Screw thread minor diameter (mm) — lower bound of hole
d_major = Screw thread major diameter (mm) — maximum hole giving minimum engagement
f_engagement = Engagement factor (0.50–0.75 for steel; 0.65–0.85 for aluminium; 0.30–0.50 for plastics)
Simplified rule (steel sheet, Type B screw):
d_pilot ≈ 0.85 × d_major (for steel t ≤ 3 mm)
d_pilot ≈ 0.90 × d_major (for steel t = 3–6 mm)
d_pilot = 0.85 × 4.8 = 4.08 mm → specify 4.1 mm drill
Over-size hole (e.g., 4.5 mm) reduces thread engagement by 50%+ and may halve pull-out strength.
Under-size hole increases driving torque above screw torsional capacity — head twist-off failure risk.
| Screw Size | Thread Major Ø (mm) | Pilot Hole — 0.5–1.0 mm steel | Pilot Hole — 1.0–2.0 mm steel | Pilot Hole — 2.0–3.2 mm steel | Pilot Hole — 3.2–4.8 mm steel | Min Screw Length in Steel |
|---|---|---|---|---|---|---|
| ST 2.2 | 2.20 | 1.6 mm | 1.8 mm | — | — | 9.5 mm |
| ST 2.9 | 2.90 | 2.1 mm | 2.4 mm | 2.5 mm | — | 9.5 mm |
| ST 3.5 | 3.53 | 2.7 mm | 2.9 mm | 3.0 mm | — | 9.5 mm |
| ST 4.2 | 4.22 | 3.3 mm | 3.5 mm | 3.6 mm | 3.7 mm | 12.7 mm |
| ST 4.8 | 4.80 | 3.9 mm | 4.0 mm | 4.1 mm | 4.2 mm | 12.7 mm |
| ST 5.5 | 5.49 | 4.5 mm | 4.6 mm | 4.8 mm | 4.9 mm | 16.0 mm |
| ST 6.3 | 6.35 | 5.1 mm | 5.4 mm | 5.5 mm | 5.6 mm | 19.0 mm |
| ST 8.0 | 8.00 | — | 6.8 mm | 7.0 mm | 7.1 mm | 25.4 mm |
Submit your BOM, substrate type, thread form, head type, drive, coating, and quantity for a documented RFQ within 24 hours.
Head Profiles &
Standards Compliance
Self-tapping screw dimensions — thread major and minor diameter, thread pitch, head geometry, drive recess, and point configuration — are fully defined by ASME B18.6.4 (inch), ISO 1481–1483 (metric), DIN 7971–7973, and DIN 7504 / EN ISO 15480 for self-drilling types. All applicable standards are supported at RR Hydraulic with full certification.
Submit thread type, head profile, drive, material, coating, and quantity to sales@rrhydraulics.com for a fully certified commercial offer.
2.1 — ISO / DIN Metric Self-Tapping Screw Dimensional Table
The following table provides dimensional data for metric Type B (ISO 1482 / DIN 7972) and self-drilling (DIN 7504 / EN ISO 15480) self-tapping screws — the two most commonly specified types in European and global EPC industrial projects.
| Designation | Thread Major Ø (mm) | Thread Pitch (mm) | Thread Minor Ø (mm) | Pan Head Dia (mm) | Pan Head Ht (mm) | CSK Head Dia (mm) | Hex Head WAF (mm) | Standard Length Range (mm) |
|---|---|---|---|---|---|---|---|---|
| ST 2.2 | 2.20 | 0.80 | 1.56 | 4.2 | 1.6 | 4.2 | — | 6.5 – 25 |
| ST 2.9 | 2.90 | 1.06 | 2.08 | 5.6 | 2.1 | 5.6 | — | 9.5 – 38 |
| ST 3.5 | 3.53 | 1.27 | 2.56 | 6.9 | 2.6 | 6.9 | — | 9.5 – 50 |
| ST 3.9 | 3.91 | 1.27 | 2.87 | 7.5 | 2.8 | 7.5 | — | 9.5 – 50 |
| ST 4.2 | 4.22 | 1.41 | 3.10 | 8.2 | 3.1 | 8.2 | 7 | 9.5 – 70 |
| ST 4.8 | 4.80 | 1.59 | 3.53 | 9.5 | 3.5 | 9.5 | 8 | 9.5 – 100 |
| ST 5.5 | 5.49 | 1.81 | 4.06 | 10.7 | 4.0 | 10.7 | 10 | 13 – 100 |
| ST 6.3 | 6.35 | 1.81 | 4.72 | 12.1 | 4.6 | 12.1 | 10 | 16 – 120 |
| ST 8.0 | 8.00 | 2.12 | 5.92 | 15.0 | 5.6 | 15.0 | 13 | 19 – 150 |
| ST 9.5 | 9.53 | 2.12 | 7.29 | 18.0 | 6.8 | 18.0 | 16 | 25 – 150 |
2.2 — Self-Drilling Screw (TEK) Dimensional and Class Table
| TEK Class | Max Steel Thickness (mm) | Drill Tip Length (mm) | Common Screw Sizes | Typical Application | Min Drive Speed (rpm) |
|---|---|---|---|---|---|
| TEK 1 | Up to 1.6 mm | 9.5 | ST 3.5 – ST 4.8 | Thin cladding, instrument panels, sheet metal | 2500 |
| TEK 2 | Up to 4.0 mm | 12.7 | ST 4.2 – ST 5.5 | Medium-gauge steel, structural sub-framing | 2000 |
| TEK 3 | Up to 6.4 mm | 15.9 | ST 4.8 – ST 6.3 | Heavy-gauge steel, purlin-to-rafter | 1500 |
| TEK 4 | Up to 9.5 mm | 19.1 | ST 5.5 – ST 8.0 | Structural steel, heavy sections, columns | 1200 |
| TEK 5 | Up to 12.7 mm | 25.4 | ST 6.3 – ST 9.5 | Very heavy steel, HSS sections, plates | 1000 |
2.3 — Head Profile Types for Self-Tapping Screws
Pan Head
Rounded domed head with flat bearing face — maximum bearing area, suitable for most general enclosure and sheet metal applications. Per ISO 1481 (slotted), ISO 7045 (Phillips/Pozi). Bearing face distributes load over the widest area of thin sheet material, minimising pull-through risk. Most common head type in EPC instrumentation enclosure assembly.
Countersunk (Flat) Head
90° or 82° conical head for flush or below-flush installation. Per ISO 1482 (slotted), ISO 7046 (Phillips/Pozi), DIN 7972. Requires a countersunk pilot hole in the outer sheet for correct seating. Used where a flush surface is required — cable tray floor plates, equipment access panels, and architectural cladding trim. Pull-through resistance is reduced vs pan head — verify for thin material.
Hex Washer Head (HWH)
Hexagonal head with an integral washer bearing face — wrench drive, maximum torque capacity, and large washer bearing area combined in a single component. The standard head for self-drilling TEK screws in structural cladding, roofing, and decking. Often supplied with a bonded EPDM sealing washer beneath the metal washer for weather-resistant installation.
Hex Head (Plain)
Standard hexagonal head without integral washer — driven by hex wrench or socket. Used with separate steel or EPDM washers where the washer specification must be controlled independently of the head. Per DIN 7504 hex variants. Provides maximum torque transmission and is standard for structural self-drilling TEK screws in purlin-to-rafter and cladding rail connections.
Bugle Head
Curved underside taper between head and shank — the curved profile distributes load gently into the substrate without tearing the surface fibres. Specifically designed for drywall (gypsum board), fibre cement board, and timber-frame applications in EPC modular building and industrial shelter construction. Prevents the head from pulling through the relatively soft board surface.
Truss Head
Extra-wide, low-profile domed head — maximum bearing area with minimum projection above the surface. Prevents pull-through in thin sheet metal and aluminium cladding under wind uplift and vibration loads. The large bearing area distributes load over a greater sheet area, effectively increasing pull-through resistance without a separate washer. Standard for light-gauge steel cladding in EPC instrument shelters and modular buildings.
2.4 — Applicable Standards and Compliance Framework
ASME B18.6.4
Thread forming and thread cutting tapping screws — inch series. Defines thread types A, B, C, and AB with dimensional data, head profiles, drive recess types, and material requirements for inch-series self-tapping screws in North American and ASME-coded EPC projects. Companion standard: ASME B18.6.3 for machine screws.
ISO 1481 / 1482 / 1483
Metric slotted self-tapping screws: ISO 1481 (Type A, slotted pan), ISO 1482 (Type B, slotted pan), ISO 1483 (Type C, slotted pan). Thread forms, head geometry, and dimensional tolerances for metric self-tapping screws in European and Asian EPC, industrial assembly, and structural cladding projects.
DIN 7971 / 7972 / 7973
DIN 7971: slotted pan head tapping screws Type A. DIN 7972: slotted pan head tapping screws Type B. DIN 7973: slotted countersunk head tapping screws. Legacy German standards still widely specified in European plant maintenance and replacement procurement. Dimensionally aligned with ISO 1481–1483 equivalents.
DIN 7504 / EN ISO 15480
Self-drilling tapping screws with hexagonal flange head and reduced shank. DIN 7504 covers the full range of drill point types (K, M, N, P) and head profiles. EN ISO 15480 is the international standard. The governing standards for structural self-drilling TEK screws in steel cladding, roofing, and decking applications worldwide.
ASTM C1513
Standard specification for steel drill screws for the application of gypsum panel products or metal plaster bases to steel studs. Governs self-drilling screws in drywall and fibre cement applications in EPC modular building, industrial shelter, and skid accommodation construction. Defines bugle head geometry, drill tip performance, and corrosion resistance for interior and exterior applications.
ISO 3506
Mechanical and physical properties of corrosion-resistant stainless steel fasteners. Property classes A2-70 (SS 304) and A4-70 / A4-80 (SS 316) for SS self-tapping screws in marine, coastal, offshore, chemical, and food-grade environments. The governing standard for SS self-tapping screw specification in corrosive service EPC supply.
ASTM A153
Zinc coating (hot-dip galvanising) on iron and steel hardware. Defines coating thickness classes A, B, C, D for HDG self-tapping screws and structural cladding fasteners. Class D (minimum 25 µm) applicable to threaded fasteners and self-tapping screws in Class B material category. HDG screws must be used with HDG or compatible nuts and washers.
Eurocode 3 Part 1-3
Design of steel structures — supplementary rules for cold-formed members and sheeting. Section 8 governs the structural design of connections using self-tapping and self-drilling fasteners in cold-formed steel construction. Defines characteristic pull-out resistance, shear bearing resistance, pull-through resistance, and combined loading interaction formulas for cladding and structural sheeting fasteners.
2.5 — Torque Reference for Self-Tapping Screw Installation
| Screw Size | Steel t = 0.5–1.0 mm (Nm) | Steel t = 1.0–2.0 mm (Nm) | Steel t = 2.0–3.2 mm (Nm) | Steel t = 3.2–4.8 mm (Nm) | Max Stripping Torque (Nm) | Recommended Power Tool Clutch (Nm) |
|---|---|---|---|---|---|---|
| ST 2.9 | 0.4–0.6 | 0.6–0.9 | 0.9–1.2 | — | 1.8 | 1.2 |
| ST 3.5 | 0.7–1.0 | 1.0–1.4 | 1.4–1.9 | — | 2.8 | 1.8 |
| ST 4.2 | 1.1–1.5 | 1.5–2.2 | 2.2–3.0 | 3.0–4.0 | 5.0 | 3.0 |
| ST 4.8 | 1.5–2.0 | 2.0–3.0 | 3.0–4.0 | 4.0–5.5 | 7.0 | 4.5 |
| ST 5.5 | — | 2.8–4.0 | 4.0–5.5 | 5.5–7.5 | 10.0 | 6.5 |
| ST 6.3 | — | 4.0–5.5 | 5.5–7.5 | 7.5–10.0 | 14.0 | 9.0 |
| ST 8.0 | — | — | 8.0–11.0 | 11.0–15.0 | 22.0 | 14.0 |
Coatings &
Manufacturing Process
Self-tapping screw material selection is primarily driven by the service corrosion environment — indoor, outdoor, coastal, marine, or chemical process exposure. RR Hydraulic manufactures self-tapping screws in all standard and corrosion-resistant grades with full EN 10204 material traceability and ISO 3506 certification for SS grades.
3.1 — Material Grade Overview and Mechanical Properties
| Material / Grade | Spec | Core Hardness | Surface Hardness | Tensile Strength | Temp Range (°C) | Corrosion Resistance | Primary Application |
|---|---|---|---|---|---|---|---|
| Case-Hardened CS | ASME B18.6.4 / ISO | 28–38 HRC | 45–55 HRC (case) | 600–900 MPa | −20 to +300 | Low (coating req.) | General sheet metal — must be coated |
| Low-Carbon CS (Class 1) | ISO / DIN standard | ≤20 HRC | ≤30 HRC (case) | 380–520 MPa | −20 to +200 | Low (coating req.) | Light gauge sheet metal, drywall |
| Medium-Carbon CS (Class 2) | ISO / DIN standard | 38–45 HRC | 50–58 HRC (case) | 700–1000 MPa | −20 to +300 | Low (coating req.) | Heavy gauge steel, structural TEK |
| A2-70 (SS 304) | ISO 3506 | — | Max 250 HV | 700 MPa | −196 to +300 | Good | Indoor/outdoor non-chloride; food/pharma |
| A4-70 (SS 316) | ISO 3506 | — | Max 250 HV | 700 MPa | −196 to +300 | Very Good | Marine, coastal, offshore, chemical |
| A4-80 (SS 316 SH) | ISO 3506 | — | Max 320 HV | 800 MPa | −196 to +300 | Very Good | High-strength marine and offshore cladding |
| Duplex 2205 | UNS S31803 | — | Max 293 HB | 620 MPa | −50 to +315 | Excellent | Offshore deck, subsea, sour + chloride |
| Aluminium (Al Mg3) | ISO 7049 | — | Soft | 150–200 MPa | −200 to +120 | Good (anodised) | Non-magnetic, lightweight, aluminium assemblies |
| Brass (CuZn37) | ISO 8839 | — | Soft | 380 MPa | −200 to +120 | Good (non-chloride) | Non-magnetic, electrical, decorative panels |
| Nylon PA66 | ISO 7049 | — | Very soft | — | −40 to +120 | Excellent | Electrical isolation, non-magnetic, GRP |
3.2 — Corrosion Resistance by Material and Environment
| Material | Inland Industrial | Coastal (<1 km sea) | Marine / Offshore | Seawater Immersed | Chloride Process | UV / Weathering | Treated Timber (CCA/ACQ) |
|---|---|---|---|---|---|---|---|
| CS + Zinc Electroplate | Good | Fair | Poor | Poor | Poor | Fair | No |
| CS + Galvanised (HDG) | Very Good | Good | Fair | Fair | Poor | Good | Good (≥85µm) |
| CS + Geomet / Dacromet | Excellent | Very Good | Good | Fair | Fair | Very Good | Very Good |
| A2-70 (SS 304) | Excellent | Good | Fair (pitting) | Poor | Poor (SCC) | Excellent | Excellent |
| A4-70 (SS 316) | Excellent | Excellent | Very Good | Good | Good | Excellent | Excellent |
| A4-80 (SS 316 SH) | Excellent | Excellent | Very Good | Good | Good | Excellent | Excellent |
| Duplex 2205 | Excellent | Excellent | Excellent | Excellent | Excellent | Excellent | Excellent |
| Aluminium (anodised) | Excellent | Good | Fair | Poor | Poor | Excellent | Good |
| Nylon PA66 | Excellent | Excellent | Excellent | Excellent | Good | Fair (UV) | Excellent |
3.3 — Surface Finish and Coating Options
| Finish | Specification | Coating Thickness (µm) | Salt Spray (h) | Treated Timber OK? | Sealing Washer Compatible? | Typical Application |
|---|---|---|---|---|---|---|
| Plain / Bright | As-manufactured | — | <24 | No | Yes | Indoor dry assembly only; not for EPC site use |
| Black Phosphate | MIL-DTL-13924 | 1–2 | 24–72 | No | Yes | Indoor panel assembly; short-term storage |
| Zinc Electroplate | ASTM B633 / ISO 4042 | 5–25 | 72–200 | No | Yes | General EPC enclosure; inland industrial |
| Yellow Zinc Chromate | ASTM B633 Type III | 5–25 + chromate | 200–500 | No | Yes | Enhanced corrosion; standard CS TEK screws |
| Hot Dip Galvanised (HDG) | ASTM A153 / ISO 1461 | 25–85 | 1000+ | Yes (≥85 µm) | Yes — HDG washer matched | Structural cladding, roofing, treated timber |
| Geomet / Dacromet | ISO 10683 | 8–12 | 1000–1500 | Yes | Yes | Roofing, coastal structural; no thread build-up |
| EPDM Bonded Washer | DIN 7504K / BS 5427 | Screw + EPDM washer | Per screw coating | Per screw base | N/A — is the washer | Weatherproof roofing and cladding standard |
| Passivation (SS only) | ASTM A380 / A967 | Passive layer | 500–2000+ | Excellent | Yes | All SS A2/A4 self-tapping and TEK screws |
| Stainless + EPDM Washer | A4-70 + EPDM | SS passive | 2000+ | Excellent | N/A — integral assembly | Marine, offshore, coastal roofing; highest spec |
3.4 — Manufacturing Process
3.4.1 — Cold Heading and Thread Rolling
Self-tapping screws are manufactured by cold heading the head and point from wire stock, followed by thread rolling to form the self-tapping thread profile. The unique thread geometry — coarser pitch, sharper thread crest, and cutting point or flute — is formed in precision thread-rolling dies specific to each screw type (A, B, C, TEK drill point). Case hardening is applied after thread rolling for carbon steel grades to harden the surface to 45–58 HRC while maintaining a ductile core — providing the thread-cutting capability without brittleness.
3.4.2 — Case Hardening Process
Carbon steel self-tapping screws must be case-hardened to provide the surface hardness necessary to cut or form threads in steel, aluminium, and other metals. The case hardening process and resulting hardness requirements:
- Surface hardness: 45–55 HRC (Type A, B) or 50–58 HRC (TEK drill point) — must exceed the hardness of the substrate material to form or cut threads effectively
- Core hardness: 28–38 HRC — maintains ductility to resist screw fracture under torsional installation stress
- Case depth: Sufficient to maintain surface hardness through the full thread engagement depth; minimum case depth checked by metallographic cross-section per DIN EN ISO 4507
- Heat treatment verification: Vickers hardness testing per ISO 6507 on sampled lot; surface and core reported on dimensional and mechanical inspection report
- Post-heat treatment: Hydrogen embrittlement relief baking may be required after electroplating on high-hardness case-hardened screws; verify per ASTM F1941 if zinc electroplating is applied
3.4.3 — EPDM Sealing Washer Assembly
TEK screws for roofing and external cladding are typically supplied with a factory-assembled EPDM (Ethylene Propylene Diene Monomer) rubber sealing washer bonded to a steel backing washer. The washer assembly seals the penetration point against weather ingress. Engineering requirements for EPDM washer assemblies:
- EPDM compound must be UV-resistant and ozone-resistant for exposed outdoor service life of 25+ years
- EPDM washer must not be over-compressed during installation — the correct clutch setting prevents washer extrusion beyond the head OD (visible indicator of over-torquing)
- Steel backing washer must match the screw coating specification (HDG backing washer with HDG screw; SS backing washer with SS screw) to prevent galvanic coupling between washer and screw
- EPDM colour coding: grey (standard); black (high-UV resistance); red (EPDM/bitumen-resistant for modified bitumen roofing membranes)
Industry Applications
& Documentation
RR Hydraulic maintains full traceability from raw wire stock to final packed shipment on all self-tapping screw orders. Dimensional inspection, hardness certificates, coating thickness reports, pull-out test data, EN 10204 MTRs, and complete EPC export documentation packages are standard on all project-grade supply.
4.1 — Inspection & QC Protocol
4.2 — EN 10204 Material Test Certificate Requirements
| Certificate | Content | Signatory | EPC Requirement | When Mandatory |
|---|---|---|---|---|
| 2.1 | Conformity declaration only | Manufacturer | Non-critical, commercial supply | General commercial hardware procurement |
| 2.2 | Non-specific test results | Manufacturer | Standard EPC cladding, enclosure, panel | General EPC self-tapping screw supply |
| 3.1 | Heat-traceable mech + chem; specific to wire lot | Manufacturer’s authorised QC Inspector | Structural cladding, offshore, SS marine | TEK structural, SS A4-70/A4-80, coastal/marine supply |
| 3.2 | 3.1 + countersigned by TPI | Manufacturer + SGS / BV / Lloyds | Critical offshore, sour, nuclear | Offshore decking, duplex grades, nuclear secondary |
4.3 — Applications by Industry
EPC — Instrument Shelters & Cabins
Type B or TEK Class 1 self-tapping screws in ST 4.8 or ST 5.5, zinc-plated or Geomet-coated, for light-gauge steel panel assembly. SS A4-70 mandatory for coastal and offshore instrument shelters. Pan head for internal panels; hex washer head with EPDM washer for external cladding joints. Power driver clutch setting critical to prevent over-torque on 0.8 mm sheet.
Industrial Roofing & Wall Cladding
TEK Class 2–4 self-drilling screws with hex washer head and EPDM sealing washer for structural steel purlin-to-rafter connection and profiled metal roof sheeting. Geomet or HDG coating for standard projects; SS A4-70 + EPDM for coastal and marine-adjacent sites. Fastener layout designed per Eurocode 3 Part 1-3 for wind uplift at 1.5× design load — minimum screw count and spacing per structural engineer’s specification.
Offshore Platform Cladding
All self-tapping and self-drilling screws on offshore topsides must be minimum SS A4-70 — carbon steel with any coating degrades rapidly in continuous marine chloride atmosphere. Duplex 2205 specified in splash zone and wave-loading cladding zones. EPDM sealing washers black (high-UV) grade. EN 10204 3.1 minimum with PMI verification on all SS lots. DNV / Lloyds third-party inspection on structural cladding screw supply.
Cable Tray & Trunking Assembly
Type B or Type C self-tapping screws (ST 3.5–ST 4.8) for cable tray fabrication and trunking joint assembly. Type C preferred where machine screw re-entry on maintenance is required. A4-70 SS for cable trays in pump rooms, battery rooms, and outdoor/submerged cable duct systems. Spanner-head or hex socket drive for organised cable management environments where Phillips drive debris contamination on cables is a risk.
Modular Building & Skid Fabrication
TEK screws in ST 4.8–ST 6.3 for steel stud framing of EPC modular buildings, control rooms, substations, and accommodation modules. Bugle head for internal drywall; hex washer head with EPDM washer for external panel joints. Treated timber used in some modular building applications — mandatory HDG ≥85 µm or SS A4-70 for all screws into CCA/ACQ-treated framing members.
Pipeline Insulation Cladding
Self-tapping screws (ST 3.5–ST 4.8) in Geomet or SS A4-70 for aluminium jacketing band fastening on insulated pipelines and equipment. Screw must penetrate aluminium cladding (1.0–1.5 mm) and engage the overlapping sheet — TEK Class 1 or standard Type A for this thin gauge. SS A4-70 mandatory for cryogenic pipeline insulation cladding in LNG service (liquid nitrogen / LNG temperatures).
4.4 — Export Packaging Specification
- Self-tapping screws bulk-packed in polybags per screw size, thread type, head type, drive, length, and coating — prevents mixing and enables direct BOM-based picking at project site
- VCI (Volatile Corrosion Inhibitor) poly bag packaging for all plain, phosphated, and zinc-plated carbon steel screws — prevents red rust formation during ocean freight and extended site storage
- TEK screws with pre-assembled EPDM sealing washers: individual screw packaging or compartmented trays to prevent washer damage and deformation during bulk transit
- Lot tagging: each polybag or box labelled with screw designation, thread size, length, material/grade, surface finish, TEK class (where applicable), heat/lot number, quantity, and PO item reference
- BOM kit packaging available: multi-compartment trays with each screw size / type in a labelled compartment — eliminates mis-picking errors in large EPC enclosure or shelter assembly kit deliveries
- Outer crating: ISPM-15 heat-treated timber crates for all international export; inner cartons labelled per UN packaging requirements for coated fastener commodity classification
- Documentation: packing list, EN 10204 MTC, coating certificate, pull-out test report, and FAI report enclosed with each lot — 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 | Wire/bar stock lot traceable |
| 02 | Chemical Composition Report | Wire lot lab analysis | Mandatory — 3.1 / 3.2 orders | Per ISO 898-1 / ISO 3506 chemistry |
| 03 | Mechanical Properties Report | UTS, hardness, proof strength | Mandatory — 3.1 / 3.2 orders | Core + surface hardness per grade |
| 04 | Hardness Test Report | ISO 6507 Vickers / ASTM E18 | Mandatory — CS case-hardened lots | Surface (HRC) and core (HRC) both reported |
| 05 | Case Depth Report | DIN EN ISO 4507 | Conditional — structural / TEK supply | Metallographic cross-section measurement |
| 06 | Dimensional Inspection Report | Per ISO / DIN / ASME B18.6.4 | Mandatory | Thread, head, drive recess, length |
| 07 | Pull-Out Strength Test Report | Eurocode 3 Part 1-3 / manufacturer spec | Mandatory — structural TEK supply | Test in representative substrate; failure load |
| 08 | Drive Torque / Strip Torque Report | ASME B18.6.4 / DIN 7972 | Conditional — EPC structural / TEK | Driving and stripping torque in representative steel |
| 09 | TEK Drill Tip Performance Test | DIN 7504 / EN ISO 15480 | Mandatory — all TEK / self-drilling supply | Drill-through time in rated steel thickness |
| 10 | Surface Finish / Coating Certificate | ISO 4042 / ASTM A153 / ISO 10683 | Mandatory — all coated supply | Thickness + salt spray hours per lot |
| 11 | EPDM Washer Quality Certificate | DIN 7504K / BS 5427 / manufacturer spec | Conditional — roofing / TEK with washer | Compression set; UV resistance; EPDM grade |
| 12 | PMI Report (XRF) | Per lot — SS / duplex grades | Mandatory — SS and duplex supply | A2-70 vs A4-70 differentiation |
| 13 | First Article Inspection (FAI) Report | Project-specific format | Mandatory — new configurations / first lots | Released before batch production |
| 14 | TPI Witness Certificate | SGS / BV / DNV / Lloyds | Conditional — EN 10204 3.2 / offshore | Co-witness at manufacturer works |
| 15 | Treated Timber Compatibility Statement | Coating compliance declaration | Conditional — CCA/ACQ timber projects | HDG ≥85µm / Geomet / SS A4-70 confirmed |
| 16 | ISO 9001:2015 Certificate | Third-party QMS certification | Mandatory — EPC projects | Scope covers self-tapping screw manufacture |
| 17 | Country of Origin Certificate | Chamber of Commerce | Mandatory — all export | HS tariff 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 and thread rolling process control, case hardening heat treatment verification, TEK drill tip performance testing, dimensional inspection, coating process QC, and full lot traceability. Mandatory for EPC and structural project procurement qualification. RR Hydraulic holds current ISO 9001:2015 certification covering self-tapping screw manufacture.
ISO 10474
Steel and steel products — inspection documents. Legacy standard from which EN 10204 certificate types derive. Some EPC project specifications reference ISO 10474 Type 2.2 or 3.1.B for fastener supply — these map to EN 10204 2.2 and 3.1 respectively. RR Hydraulic can provide documentation cross-reference in either format on project request.
Eurocode 3 Part 1-3
Design of steel structures — cold-formed members and sheeting, Section 8: fasteners. The governing structural design standard for self-tapping and self-drilling screw connections in steel cladding and profiled sheeting. Defines pull-out, pull-through, and bearing resistance calculation methods used by structural engineers to establish minimum screw count and placement in roofing and cladding design.
ISO 4413
Safety requirements for hydraulic fluid power systems. Self-tapping screws used in hydraulic power unit (HPU) enclosure panels, junction boxes, and control cabinet mounting must meet ISO 4413 cleanliness standards for any fastener debris that could contaminate the hydraulic system. For HPU enclosure work, specify SS A4-70 self-tapping screws to prevent corrosion-generated particulate contamination in hydraulic system environments.
Submit your BOM, thread type, substrate, head profile, coating, and quantity to RR Hydraulic for a complete, certified commercial offer.