RFQ Today
Certifications available: EN 10204 3.1 / 3.2 MTRs, ISO 3506 SS certification, ASTM A153 HDG, Eurocode 3 Part 1-3 pull-out test data, Third-Party Inspection, and complete EPC export documentation packages.
Self-Drilling Screws
A world-class technical reference for EPC contractors, structural and civil engineers, procurement heads, TPI inspection agencies, and global project buyers specifying self-drilling screws in structural steel cladding, roofing, purlins, HVAC ductwork, and light steel framing across Oil & Gas, Power Generation, Petrochemical, Infrastructure, and Offshore Construction sectors.
Drill Point Classes
& Structural Behaviour
Self-drilling screws are fasteners that combine an integral drill bit point with a self-tapping thread — penetrating the substrate, drilling a clearance hole, and forming or cutting a mating thread in a single uninterrupted operation, without any pre-drilling or pre-tapping. They are the primary structural fastener in cold-formed steel construction, metal cladding, roofing, and decking across the global EPC industry.
1.1 — Technical Definition and Functional Role
A self-drilling screw (commonly called a TEK screw, drill screw, or Teks® screw) consists of three functional zones: a drill point tip that removes material to create a clearance hole; a thread-forming or thread-cutting zone that engages the substrate after penetration; and a threaded shank that provides the clamping load. The critical engineering advantage over conventional self-tapping screws is the elimination of the pre-drilling step — reducing installation time by 40–60% in structural cladding, roofing, and framing applications.
In EPC structural construction, self-drilling screws are specified for: metal roof and wall cladding to structural steel purlins and girts (TEK Class 3–5); light gauge steel stud framing of modular buildings, substations, control buildings, and accommodation modules (TEK Class 1–2); steel decking and floor plate attachment to structural beams; HVAC ductwork fabrication and support bracket attachment; pipe support secondary steelwork; cable tray support systems; and equipment shelter fabrication. Their pull-out and shear strength are structural design parameters governed by Eurocode 3 Part 1-3, AS 4100, and AISC 360.
RR Hydraulic manufactures and exports self-drilling screws under all applicable international standards with full EN 10204 material traceability and TPI capability.
1.2 — TEK Class System: Drill Penetration Capacity
The TEK class system defines the maximum total steel thickness the drill point can penetrate without burning out before thread engagement begins. TEK class is the primary engineering selection parameter for self-drilling screws in structural steel connections — it governs whether the screw will successfully penetrate all steel members in the connection stack before the drill point is consumed.
| TEK Class | Max Total Steel (mm) | Max Total Steel (gauge) | Drill Tip Length (mm) | Drill Tip Flute Count | Typical Screw Sizes | Typical Structural Application | Min Drive Speed (rpm) |
|---|---|---|---|---|---|---|---|
| TEK 1 | ≤ 1.6 | ≤ 16 ga | 9.5 | 2 | ST 3.5–ST 4.8 | Thin cladding, drywall track, instrument shelter panels | 2500 |
| TEK 2 | ≤ 4.0 | ≤ ¼” | 12.7 | 2 | ST 4.2–ST 5.5 | Medium-gauge sub-framing, cladding rail to light purlin | 2000 |
| TEK 3 | ≤ 6.4 | ≤ ¼” | 15.9 | 3 | ST 4.8–ST 6.3 | Heavy purlin-to-rafter, structural framing connection | 1500 |
| TEK 4 | ≤ 9.5 | ≤ ⅜” | 19.1 | 3 | ST 5.5–ST 8.0 | Structural steel primary members, columns, beams | 1200 |
| TEK 5 | ≤ 12.7 | ≤ ½” | 25.4 | 4 | ST 6.3–ST 9.5 | Very heavy structural steel, HSS sections, base plates | 1000 |
1.3 — Drill Point Geometry Types
Type K — Standard 2-Flute Drill Point
Standard two-flute twist drill geometry. Used in TEK Class 1 and 2 screws for thin to medium gauge steel. Chip evacuation is adequate for thin materials. The most common drill point in general EPC structural cladding and light framing. Per DIN 7504-K / EN ISO 15480.
Type L — Long 2-Flute Drill Point
Extended drill point length relative to the thread start — provides additional drill depth before thread engagement. Used where multiple sheet layers must be penetrated before the thread zone reaches the substrate (e.g., insulated cladding with a liner sheet and structural facing sheet). Prevents thread engagement in the outer layer before penetrating the structural member.
Type N — 3-Flute Drill Point (TEK 3–4)
Three-flute drill tip geometry for improved chip evacuation and reduced heat generation when drilling through heavier gauge steel (TEK Class 3–4). The additional flute reduces torque peaks during penetration and extends drill tip life in production installation environments. Per DIN 7504-N.
Type P — 4-Flute High-Performance Drill Point (TEK 5)
Four-flute drill geometry for maximum steel penetration capacity (TEK Class 5, up to 12.7 mm total steel). Used in structural connections to primary steel — columns, beams, and base plate connections. Highest chip evacuation efficiency; lowest heat buildup; longest drill tip life of all point types. Per DIN 7504-P.
Winged Drill Point (ETA-Approved)
Drill point with two outboard wings that ream a clearance hole in the outer timber layer wider than the screw thread before the wings break off on contact with the steel substrate — allowing the thread to engage only the steel without binding in the timber. Used in timber-to-steel connections (timber purlin, timber blocking to steel). Common in EPC modular building timber/steel hybrid structures.
Aluminium Drill Point
Specially hardened drill point geometry optimised for drilling through aluminium cladding and aluminium structural members without heat staining or galling — a risk with standard steel-optimised drill geometry in soft aluminium. Used in aluminium-clad EPC instrument shelters, modular buildings, and lightweight offshore accommodation structures.
1.4 — Structural Load Characteristics
Pull-Out Resistance (Axial)
Axial tensile resistance of the screw thread in the base metal (structural section). Governed by screw thread major diameter, thread pitch, engaged thread length in the base metal, and base metal yield strength. Pull-out resistance per Eurocode 3 Part 1-3 Clause 8.3.2. Self-drilling screws exhibit higher pull-out than self-tapping screws (no pilot hole — tighter thread engagement) in equivalent steel thickness.
Pull-Through Resistance (Head)
Resistance to the screw head (and washer) pulling through the outer sheet under uplift loading. Governed by head/washer diameter, sheet thickness, and sheet yield strength. Per Eurocode 3 Part 1-3 Clause 8.3.3. In roofing and cladding design, wind uplift forces often govern the fastener count — pull-through must be checked for each sheet thickness and screw head/washer combination.
Shear Resistance (Lateral)
Lateral load capacity in the plane of the connected sheet. Governed by screw diameter, sheet thicknesses (both connected members), and material yield strengths. Net section bearing and shear-out failure modes per Eurocode 3 Part 1-3. In wall cladding, wind pressure and earthquake loads create in-plane shear — shear capacity must be verified for the specified screw grid layout.
Combined Load Interaction
In most practical cladding and roofing applications, self-drilling screws carry simultaneous pull-out (from wind uplift) and shear (from wind pressure). The combined load interaction per Eurocode 3 Part 1-3 Clause 8.3.5: (F_t / F_t,Rd)^α + (F_v / F_v,Rd)^α ≤ 1.0, where α = 1.0 for self-drilling screws. This interaction governs fastener count in high-wind-zone designs.
Fatigue Under Cyclic Wind Loading
Cladding and roofing fasteners in high-cycle wind environments (coastal, elevated exposure categories) experience cyclic pull-through and pull-out loading. Self-drilling screws with EPDM sealing washers can exhibit washer creep under sustained load — EPDM washer quality (low compression set per ISO 815) is critical for maintaining long-term sealing integrity and residual clamping force.
Thermal Cycling and Differential Movement
Profiled metal cladding panels expand and contract thermally — in a 50°C temperature range, a 6-metre steel panel moves approximately 3.6 mm. Fixed-end self-drilling screws resist this movement, generating fatigue stress in the sheet around the fastener hole. Correct installation allows for thermal movement: screws in elongated slots at one end of each panel, with fixed screws at the other end only.
1.5 — Pull-Out Strength Calculation — Eurocode 3 Part 1-3
d = Nominal thread diameter of screw (mm)
t₂ = Thickness of member in which thread is engaged — base steel (mm)
f_u2 = Ultimate tensile strength of base steel (MPa)
γ_M2 = Partial safety factor = 1.25 (Eurocode 3 Part 1-3)
Pull-Through Resistance (Clause 8.3.3):
F_t,Rd = d_w × t₁ × f_u1 / γ_M2
d_w = washer/head diameter (mm); t₁ = outer sheet thickness (mm); f_u1 = outer sheet UTS (MPa)
Pull-out: F_t,Rd = 0.65 × 5.5 × 2.5 × 350 / 1.25 = 2,503 N = 2.50 kN
Pull-through (EPDM washer d_w = 18 mm): F_t,Rd = 18 × 0.7 × 350 / 1.25 = 3,528 N = 3.53 kN
Pull-out governs (2.50 kN). Design wind uplift per screw ≤ 2.50 / 1.50 = 1.67 kN/screw (service load at γ_F = 1.50).
| Application | Safety Factor | Governing Standard | Key Design Requirement |
|---|---|---|---|
| Standard roofing / cladding | γ_M2 = 1.25 (EC3) | Eurocode 3 Part 1-3 | Pull-out + pull-through + shear interaction check |
| Structural steel framing connections | γ_M2 = 1.25 | Eurocode 3 Part 1-3 / AISC 360 | Shear and tension in cold-formed section |
| Offshore platform cladding | γ_M2 = 1.25 × DAF | DNV-ST-N001 / EC3 | Dynamic amplification factor; SS A4-70 minimum |
| High-wind-zone roofing (>150 km/h) | γ_M2 = 1.50 recommended | AS 4600 / local code | Increased fastener count; TEK class verified |
| Seismic zone cladding | Per seismic category | ASCE 7 / ISO 3010 | Ductility requirement; SS or HDG in humid zones |
| ATEX zone shelter cladding | γ_M2 = 1.25 | IEC 60079 / Eurocode | SS screws mandatory; no zinc electroplate |
| Cryogenic / LNG plant cladding | γ_M2 = 1.25 | Project spec / Eurocode | SS A4-70; check embrittlement at −165°C |
Submit your TEK class, structural steel thickness schedule, head type, coating, and quantity for a documented RFQ within 24 hours.
Head Profiles &
Standards Compliance
Self-drilling screw dimensions are governed by DIN 7504 / EN ISO 15480 (metric), ASME B18.6.4 (inch series), ISO 10666, and AS 3566. Head profile, thread form, drill tip geometry, and EPDM washer specification are all critical parameters. All applicable standards are supported at RR Hydraulic with full project certification.
Submit TEK class, thread size, head type, drive, material, coating, and quantity to sales@rrhydraulics.com for a fully certified offer.
2.1 — DIN 7504 / EN ISO 15480 Self-Drilling Screw Dimensional Table
The following table provides key dimensional data for hexagonal washer head self-drilling screws per DIN 7504 / EN ISO 15480 — the primary standard for structural cladding and roofing self-drilling screws in European and globally specified EPC projects.
| Designation | Thread Ø d (mm) | Thread Pitch (mm) | Hex WAF (mm) | Integral Washer OD (mm) | Head Height (mm) | EPDM Washer OD (mm) | TEK Class | Standard Lengths (mm) |
|---|---|---|---|---|---|---|---|---|
| ST 3.5×(L)-K | 3.53 | 1.27 | 8 | 8.0 | 5.5 | 12 | 1 | 13–50 |
| ST 4.2×(L)-K | 4.22 | 1.41 | 8 | 9.0 | 6.0 | 14 | 1–2 | 13–70 |
| ST 4.8×(L)-K | 4.80 | 1.59 | 8 | 10.0 | 6.5 | 16 | 1–3 | 16–100 |
| ST 5.5×(L)-N | 5.49 | 1.81 | 10 | 11.0 | 7.0 | 19 | 2–4 | 19–120 |
| ST 6.3×(L)-N | 6.35 | 1.81 | 10 | 12.0 | 7.5 | 22 | 3–4 | 25–150 |
| ST 6.3×(L)-P | 6.35 | 1.81 | 10 | 12.0 | 7.5 | 22 | 5 | 38–150 |
| ST 8.0×(L)-P | 8.00 | 2.12 | 13 | 16.0 | 9.5 | 28 | 4–5 | 38–200 |
| ST 9.5×(L)-P | 9.53 | 2.12 | 16 | 19.0 | 11.0 | 32 | 5 | 50–200 |
2.2 — Head Profile Types for Self-Drilling Screws
Hex Washer Head (HWH) — Structural Standard
Hexagonal head with integral steel washer bearing face. The standard head for structural cladding and roofing TEK screws. Driven by hex socket or hex bit — maximum torque transmission without cam-out. Integral washer provides large bearing area to distribute head load and minimise pull-through in thin outer sheets. Bonded EPDM rubber washer beneath for weatherproofing. Per DIN 7504 / EN ISO 15480.
Hex Head (No Integral Washer)
Standard hexagonal head without integral washer — used with a separate steel or EPDM washer where the washer specification must be independently controlled. Provides the highest torque transmission capacity. Used in non-weatherproofing structural connections (internal steel framing, secondary steelwork) where the EPDM sealing washer is not required.
Pan Head
Rounded dome head with flat bearing face for maximum bearing area without an integral washer. Common in lighter-gauge steel framing (TEK Class 1–2) and non-structural applications — HVAC ductwork, instrument enclosure panels, cable tray, and internal partition framing. Phillips, Pozidriv, or Torx drive depending on project specification.
Truss Head
Extra-wide low-profile dome head — maximum bearing area per head height; excellent pull-through resistance in thin outer sheets without a separate washer. Used in thin-gauge steel enclosure panels, instrument shelter wall sheeting, and modular building cladding where the large head area provides adequate pull-through capacity in 0.5–0.7 mm sheet without EPDM.
Bugle Head
Curved underside profile for gentle embedment into drywall board and fibre cement board without tearing the paper face or surface — the curved profile transitions load smoothly into the board. Per ASTM C1513. Used in EPC modular building and instrument shelter internal lining where drywall, fibre cement, or MgO board is attached to light steel studs by self-drilling screws.
Countersunk (Flat) Head
90° or 82° conical head for flush installation in countersunk applications — access panels, floor plate inserts, decorative cladding trim, and architectural facades. Requires the outer sheet to be countersunk to receive the head. Pull-through resistance is reduced compared to pan or HWH heads — must be verified for thin sheet applications under wind uplift.
2.3 — Applicable Standards and Compliance Framework
DIN 7504 / EN ISO 15480
Self-drilling tapping screws — metric. DIN 7504 defines drill point types (K, L, N, P), head profiles, thread forms, and material requirements for metric self-drilling screws in structural cladding, roofing, and framing. EN ISO 15480 is the international equivalent. The primary standard for European and global EPC structural self-drilling screw specification.
ASME B18.6.4
Thread forming and thread cutting tapping screws — inch series. Governs inch-series self-drilling screws in North American EPC projects. TEK class and drill point geometry requirements are equivalent to DIN 7504 but expressed in imperial dimensions. Thread class 2A (UNC) per ASME B1.1.
ISO 10666
Drilling screws with tapping screw thread — mechanical and performance requirements. International performance standard for self-drilling screws covering torsional strength, drive recesses, drill tip performance, and corrosion resistance. Referenced in European technical approvals (ETAs) for structural fasteners and in Eurocode 3 Part 1-3 connection design.
AS 3566
Self-drilling screws for the building and construction industries — Australian/New Zealand standard. Class 1–4 corrosion resistance classification for self-drilling screws in external construction: Class 1 (interior protected); Class 2 (interior + mild exterior); Class 3 (severe exterior — stainless or equivalent coating); Class 4 (very severe — stainless). Used in Australian, NZ, and Pacific EPC projects.
Eurocode 3 Part 1-3
Design of steel structures — supplementary rules for cold-formed members and sheeting, Section 8. The governing structural design standard for self-drilling screw connections. Defines pull-out (8.3.2), pull-through (8.3.3), shear bearing (8.3.4), and combined load interaction (8.3.5) design resistance formulas. Minimum connection requirements for structural cladding and sheeting fasteners.
ISO 3506
Mechanical and physical properties of corrosion-resistant stainless steel fasteners. Property class A4-70 (SS 316, 700 MPa UTS) and A4-80 (SS 316 strain-hardened, 800 MPa UTS) for SS self-drilling screws in marine, coastal, offshore, and chemical environments. The governing standard for SS self-drilling screw specification in corrosive EPC supply.
ASTM A153
Zinc coating (hot-dip galvanising) on iron and steel hardware. Class D (minimum 25 µm average) applies to threaded fasteners including self-drilling screws ≤12.7 mm diameter. HDG self-drilling screws are the standard for structural cladding in non-coastal EPC construction where long-term corrosion resistance is required without the premium cost of SS.
ASTM C1513
Steel drill screws for the application of gypsum panel products or metal plaster bases to steel studs. Governs bugle head self-drilling screws in light steel framing (LSF) for drywall, fibre cement, and MgO board attachment in EPC modular buildings, control rooms, accommodation modules, and substations. Defines bugle head geometry, drill tip performance, and corrosion resistance classes.
2.4 — Installation Torque Reference
| Screw Size | TEK Class | Steel t₂ = 1.0–2.0 mm (Nm) | Steel t₂ = 2.0–4.0 mm (Nm) | Steel t₂ = 4.0–6.4 mm (Nm) | Steel t₂ = 6.4–9.5 mm (Nm) | Max Strip Torque (Nm) | Clutch Setting (Nm) |
|---|---|---|---|---|---|---|---|
| ST 3.5 | 1 | 1.0–1.5 | — | — | — | 3.0 | 1.8 |
| ST 4.2 | 1–2 | 1.5–2.2 | 2.2–3.5 | — | — | 5.5 | 3.0 |
| ST 4.8 | 1–3 | 2.0–3.0 | 3.0–4.5 | 4.5–6.0 | — | 7.5 | 4.5 |
| ST 5.5 | 2–4 | 2.5–3.8 | 3.8–5.5 | 5.5–8.0 | 8.0–10.5 | 11.0 | 7.0 |
| ST 6.3 | 3–5 | — | 5.0–7.5 | 7.5–10.5 | 10.5–14.0 | 16.0 | 10.0 |
| ST 8.0 | 4–5 | — | — | 10.0–14.5 | 14.5–20.0 | 27.0 | 17.0 |
| ST 9.5 | 5 | — | — | — | 18.0–28.0 | 40.0 | 25.0 |
2.5 — EPDM Sealing Washer Specification
| EPDM Grade | Colour | Temp Range (°C) | UV Resistance | Ozone Resistance | Chemical Resistance | Typical EPC Application |
|---|---|---|---|---|---|---|
| Standard EPDM | Grey | −40 to +120 | Good | Good | Moderate | Inland industrial roofing, standard EPC cladding |
| Black EPDM (Hi-UV) | Black | −50 to +140 | Excellent | Excellent | Good | High-UV zones, tropical EPC, coastal roofing |
| Red EPDM (Bitumen-Resist.) | Red | −30 to +130 | Good | Good | Excellent (bitumen) | Modified bitumen membrane roofing |
| EPDM + Aluminium Washer | Silver/grey | −50 to +130 | Excellent | Excellent | Good | Aluminium cladding; prevents galvanic contact |
| Silicone (high-temp) | Red / white | −60 to +200 | Excellent | Excellent | Excellent | High-temperature cladding near process equipment |
| EPDM-free (metal-to-metal) | — | — | N/A | N/A | N/A | Internal non-weatherproofing structural connections only |
Coatings &
Manufacturing Process
Self-drilling screw material selection is governed primarily by the corrosion exposure category of the installation environment. RR Hydraulic manufactures self-drilling screws in all standard and corrosion-resistant grades — from case-hardened carbon steel with Geomet coating through SS A4-80 for the most aggressive offshore and coastal environments.
3.1 — Material Grade Overview and Mechanical Properties
| Material / Grade | Spec | Core HRC | Surface HRC (case) | UTS (MPa) | Temp Range (°C) | Corrosion Class | Primary EPC Application |
|---|---|---|---|---|---|---|---|
| Case-Hardened CS (Zn) | DIN 7504 / ASME B18.6.4 | 28–38 | 45–55 | 600–900 | −20 to +300 | 1–2 (inland) | Standard EPC inland/industrial cladding |
| CS + Geomet / Dacromet | ISO 10683 | 28–38 | 45–55 | 600–900 | −20 to +300 | 2–3 (moderate) | Coastal-adjacent, high-corrosion EPC sites |
| CS + HDG (ASTM A153) | ASTM A153 Class D | 28–38 | 45–55 | 600–900 | −20 to +200 | 3 (severe) | Structural cladding, treated timber adjacent |
| A2-70 (SS 304) | ISO 3506 | — | Max 250 HV | 700 | −196 to +300 | 3 (severe) | Mild coastal, food, pharma |
| A4-70 (SS 316) | ISO 3506 | — | Max 250 HV | 700 | −196 to +300 | 4 (very severe) | Marine, coastal, offshore topsides |
| A4-80 (SS 316 SH) | ISO 3506 | — | Max 320 HV | 800 | −196 to +300 | 4 (very severe) | Offshore structural, high wind-uplift coastal |
| Duplex 2205 | UNS S31803 | — | Max 293 HB | 620 | −50 to +315 | 5 (extreme) | Offshore splash zone, seawater, sour service |
| Bimetall (SS tip + CS body) | Proprietary | 28–38 (body) | 45–55 (tip) | 700–900 | −20 to +300 | 4 | SS corrosion resistance + CS drill performance |
3.2 — Corrosion Environment Classification and Material Selection
| Corrosion Category (ISO 9223) | Environment Description | EPC Site Examples | Minimum Screw Specification | EPDM Washer Spec | AS 3566 Class |
|---|---|---|---|---|---|
| C1 — Very Low | Heated interior, dry, no condensation | Indoor electrical rooms, MCC rooms | Case-hardened CS, phosphate | Not required | Class 1 |
| C2 — Low | Unheated interior, low pollution, rural | Inland EPC warehouses, substations | Case-hardened CS, zinc plate | Standard EPDM grey | Class 2 |
| C3 — Medium | Urban/industrial atmosphere, moderate SO₂ | Refineries, petrochemical plants (inland) | CS + Geomet or HDG ≥ 25 µm | Black EPDM hi-UV | Class 3 |
| C4 — High | Industrial high humidity, chemical or coastal | Coastal EPC within 5 km sea; LNG plants | CS + HDG ≥ 45 µm or A4-70 SS | Black EPDM hi-UV | Class 3–4 |
| C5-I — Very High (Industrial) | High humidity, aggressive industrial, chemical | Chemical plants, sulphur, acid service | A4-70 or A4-80 SS minimum | Black EPDM | Class 4 |
| C5-M — Very High (Marine) | High salinity, offshore topsides, splash zone | Offshore platforms, FPSOs, marine structures | A4-80 SS or Duplex 2205 | Black EPDM + SS washer | Class 4 |
| CX — Extreme | Very high salinity + industrial pollution | Offshore in tropical/high-humidity zones | Duplex 2205 or Super Duplex | Black EPDM + Duplex washer | Class 4+ |
3.3 — Surface Finish and Coating Options
| Finish | Specification | Coating Thickness (µm) | Salt Spray (h) | Drill Tip Impact | AS 3566 Class | Application |
|---|---|---|---|---|---|---|
| Plain / Bright | As-manufactured | — | <24 | None | 1 | Interior dry only; not structural cladding |
| Yellow Zinc Chromate | ASTM B633 Type III | 5–25 | 200–500 | None (thin) | 2 | General EPC inland cladding; standard CS TEK |
| Geomet 321 | ISO 10683 | 8–12 | 1000–1500 | Minimal | 3 | Coastal-adjacent EPC; no thread build-up problem |
| Geomet 500 | ISO 10683 | 8–12 | 1500–2000 | Minimal | 3–4 | Near-coastal EPC; high-performance coating |
| HDG (ASTM A153 Class D) | ASTM A153 / ISO 1461 | 25–85 | 1500+ | Slight softening of tip | 3 | Structural cladding; treated timber adjacent |
| A4-70 SS (passivated) | ASTM A380 / ISO 3506 | Passive layer | 2000+ | Reduced drill hardness* | 4 | Marine, coastal, offshore, food/pharma |
| A4-80 SS (passivated) | ASTM A380 / ISO 3506 | Passive layer | 2000+ | Better than A4-70* | 4 | High-strength offshore structural cladding |
| Bimetallic (SS tip + CS body) | Proprietary | N/A | 2000+ (body HDG) | Full CS drill performance | 4 | Offshore / coastal: SS corrosion + CS drill capacity |
* SS self-drilling screws have lower drill tip hardness than case-hardened CS — drill capacity is reduced. SS TEK screws are typically limited to TEK Class 1–2 (≤4 mm total steel). For heavier structural steel (TEK Class 3–5), specify bimetallic screws or pre-drill then use SS self-tapping screw.
3.4 — Manufacturing Process
3.4.1 — Cold Heading, Thread Rolling, and Drill Tip Forming
Self-drilling screws are manufactured in a multi-stage cold forming and machining process. The hex head, integral washer, and drive socket are formed by cold heading from wire stock. Thread rolling follows — producing the self-tapping thread with compressive residual stress at the thread root. The drill tip is then formed by precision grinding or by a secondary cold-forging operation to produce the two, three, or four-flute drill geometry specific to the TEK class. Drill tip geometry must maintain tight dimensional tolerances — drill diameter must be within 0.05 mm of the screw thread major diameter to ensure the drill creates a clearance hole before thread engagement, without leaving a step that causes thread engagement difficulty or stripping.
3.4.2 — Case Hardening
The drill tip must be hard enough to cut through the rated steel thickness before wearing out. Case hardening requirements for self-drilling screws:
- Drill tip surface hardness: 50–58 HRC — must exceed the hardness of the structural steel substrate (typically 150–250 HB / 8–25 HRC for structural steel grades S250–S550)
- Core hardness: 28–38 HRC — ductile core prevents brittle fracture under the torque peaks during drilling and thread formation
- Case depth: Must maintain the surface hardness through the full drill point geometry; measured by metallographic cross-section per DIN EN ISO 4507
- Hardness verification: Vickers or Rockwell hardness testing on sampled lot; surface and core values reported on inspection certificate
3.4.3 — EPDM Washer Bonding
EPDM sealing washers are bonded to the integral steel washer on the underside of the hex washer head. The bonding process must produce a washer assembly that does not delaminate during installation or during subsequent thermal cycling in service. Quality requirements:
- Bond strength: peel test per DIN EN ISO 8510 — EPDM rubber must tear before bond fails
- Compression set: max 25% at 70°C × 22 hours per ISO 815-1 — ensures EPDM recovers residual sealing thickness after sustained compression under the screw head
- UV resistance: no surface cracking after 2000 hours UV exposure per ISO 4892-2 for black (carbon-black-filled) EPDM grade
- EPDM dimensions: OD and thickness per screw manufacturer’s specification — not generic; undersized washers reduce pull-through resistance below the design value
Industry Applications
& Documentation
RR Hydraulic maintains full traceability from raw wire stock to final packed shipment on all self-drilling screw orders. Dimensional inspection, hardness certificates, drill tip performance test data, pull-out strength reports, coating inspection, EN 10204 MTRs, and complete EPC export documentation are standard on all project-grade supply.
4.1 — Inspection & QC Protocol
4.2 — EN 10204 Material Test Certificate Requirements
| Certificate | Content | Signatory | EPC Application | When Mandatory |
|---|---|---|---|---|
| 2.1 | Conformity declaration only | Manufacturer | Non-structural, interior, commercial | General commercial hardware procurement |
| 2.2 | Non-specific test results | Manufacturer | Standard EPC inland cladding and framing | General EPC structural cladding supply (C2–C3) |
| 3.1 | Heat-traceable mech + chem; wire lot specific | Manufacturer’s authorised QC Inspector | SS marine / offshore; structural design-verified | A4-70/A4-80 SS, coastal C4/C5, design-critical structural |
| 3.2 | 3.1 + countersigned by TPI | Manufacturer + SGS / BV / DNV / Lloyds | Offshore platform, duplex, nuclear secondary | Offshore C5-M, duplex grades, critical structural cladding |
4.3 — Applications by Industry
EPC Industrial Roofing & Wall Cladding
TEK Class 3–4 HWH self-drilling screws (ST 4.8–ST 6.3) with Geomet or HDG coating and EPDM sealing washers are the standard for single-skin and built-up profiled metal roof and wall cladding to structural steel purlins and girts. Fastener layout designed per Eurocode 3 Part 1-3 for wind uplift at 1.5× design load. For coastal EPC sites within 5 km of the sea: A4-70 SS or HDG ≥45 µm mandatory — specify project corrosion category with structural engineer before procurement.
Offshore Platform & FPSO Cladding
All self-drilling screws on offshore topsides: minimum A4-80 SS with EPDM black washer and SS backing washer. Duplex 2205 for splash zone and areas of cathodic protection influence. Bimetallic screws (SS body + hardened CS tip) for structural connections requiring TEK Class 3+ drill capacity with full SS corrosion performance. EN 10204 3.1 minimum; 3.2 with DNV / Lloyds TPI for structural cladding connections.
Light Steel Framing — Modular Buildings
TEK Class 1–2 bugle head or pan head self-drilling screws (ST 3.5–ST 4.8) in yellow zinc or Geomet finish for light gauge steel stud framing of EPC modular buildings, control rooms, accommodation modules, and substations. Bugle head for drywall and fibre cement board attachment to steel studs per ASTM C1513. HWH hex head for external cladding. Framing design per AISI S100 or Eurocode 3 Part 1-3.
HVAC Ductwork & Support Systems
TEK Class 1–2 pan head or HWH self-drilling screws in ST 3.5–ST 4.8 for HVAC ductwork fabrication (galvanised steel duct joining), insulated duct cladding attachment, and support hanger bracket-to-structural steel connections. Zinc yellow chromate or Geomet finish for indoor/protected service; SS A4-70 for process air handling in chemical or marine environments.
Petrochemical Instrument Shelters
Complete structural package for EPC instrument shelter fabrication: TEK Class 3 HWH for outer cladding to structural steel (A4-70 SS in coastal/process zone); TEK Class 1 bugle head for internal drywall and fibre cement board; TEK Class 2 HWH for cable tray support brackets. Full QC package with EN 10204 3.1 for SS lots and drill tip test certificates for all structural screws.
Power Station & Substation Buildings
TEK Class 2–4 self-drilling screws in HDG or Geomet (inland power stations) or SS A4-70 (coastal power stations) for plant building cladding. Special attention to EPDM washer quality for 30+ year design life — specify black carbon-black EPDM with UV resistance certification. Thermal expansion allowance details (fixed vs slotted screw positions) must be confirmed with structural engineer for the specified panel material and length.
4.4 — Export Packaging Specification
- Self-drilling screws bulk-packed in polybags per screw designation (thread size, TEK class, head type, material, coating, length) — prevents inter-lot mixing and enables direct site installation from pre-labelled polybags
- EPDM washer integrity protection: HWH screws with bonded EPDM washers packed with divider trays or orientation control to prevent EPDM-to-EPDM face contact in bulk bags — prevents washer distortion and delamination during shipping vibration
- VCI (Volatile Corrosion Inhibitor) poly bag packaging for all carbon steel and Geomet-coated lots — prevents oxidation of cut drill tip surfaces during ocean freight and extended site storage
- Individual lot tagging: each polybag labelled with DIN 7504 / EN ISO 15480 designation, thread size, length, TEK class, material/grade, surface finish, EPDM washer specification, heat/lot number, quantity, and PO item reference
- Multi-size BOM kit packaging available: compartmented carton with each screw type/size in a labelled section — standard delivery format for EPC modular building and shelter fabrication kits
- Outer crating: ISPM-15 heat-treated pine crates for all international export; inner cartons protected from moisture with desiccant sachets for ocean freight shipments longer than 4 weeks
- Documentation enclosed: packing list, EN 10204 MTC, coating certificate, drill tip performance test certificate, pull-out test data (structural supply), EPDM washer quality certificate, and FAI report — all 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/lot traceable to production heat |
| 02 | Chemical Composition Report | Wire lot lab analysis | Mandatory — 3.1 / 3.2 orders | Per DIN 7504 / ISO 3506 chemistry limits |
| 03 | Mechanical Properties Report | UTS, hardness (surface + core) | Mandatory — 3.1 / 3.2 orders | Drill tip HRC + core HRC per lot |
| 04 | Drill Tip Performance Test Certificate | DIN 7504 / EN ISO 15480 / ISO 10666 | Mandatory — all self-drilling supply | TEK class steel stack; penetration time; result |
| 05 | Hardness Test Report | ISO 6507 Vickers / ASTM E18 Rockwell | Mandatory — all lots | Surface + core; case depth where required |
| 06 | Dimensional Inspection Report | Per DIN 7504 / EN ISO 15480 / ASME B18.6.4 | Mandatory | Thread, head WAF/washer OD, drill tip Ø, length |
| 07 | Pull-Out Strength Test Report | Eurocode 3 Part 1-3 / ISO 10666 | Mandatory — structural cladding supply | Test in representative steel t₂; failure load |
| 08 | Pull-Through Strength Test Report | Eurocode 3 Part 1-3 | Conditional — roofing / uplift-critical | Test with EPDM washer in representative outer sheet |
| 09 | Coating / Surface Finish Certificate | ISO 10683 / ASTM A153 / ISO 4042 | Mandatory — all coated supply | Thickness + salt spray hours per lot |
| 10 | EPDM Washer Quality Certificate | ISO 815-1; ISO 4892-2; ISO 8510 | Mandatory — HWH with EPDM washer | Compression set + UV resistance + bond strength |
| 11 | PMI Report (XRF) | Per lot — SS and duplex grades | Mandatory — SS / duplex supply | A2 vs A4 grade differentiation |
| 12 | First Article Inspection (FAI) Report | Project-specific format | Mandatory — new configurations / first lots | Released before batch production |
| 13 | TPI Witness Certificate | SGS / BV / DNV / Lloyds | Conditional — 3.2 / offshore / structural | Co-witness at manufacturer works |
| 14 | Corrosion Category Compliance Statement | ISO 9223 / AS 3566 class declaration | Conditional — coastal / marine EPC | Confirms screw spec meets project corrosion category |
| 15 | ISO 9001:2015 Certificate | Third-party QMS certification | Mandatory — all EPC structural supply | Scope covers self-drilling screw manufacture |
| 16 | Country of Origin Certificate | Chamber of Commerce | Mandatory — all export | HS tariff code for customs classification |
| 17 | Packing List | Item-level per shipment | Mandatory | Cross-references lot numbers and MTC |
| 18 | Commercial Invoice | Per INCOTERMS 2020 | Mandatory | Includes HS tariff code |
| 19 | 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 qualification, cold heading, thread rolling, drill tip grinding process control, case hardening heat treatment verification, drill tip performance testing, EPDM washer bonding QC, coating process qualification, and full lot traceability. Mandatory for all EPC, offshore, and structural project procurement qualification. RR Hydraulic holds current ISO 9001:2015 certification.
Eurocode 3 Part 1-3
Design of steel structures — cold-formed members and sheeting, Section 8. The primary structural design standard for self-drilling screw connections in roofing, cladding, and light steel framing. Pull-out (8.3.2), pull-through (8.3.3), bearing (8.3.4), and combined load interaction (8.3.5) formulas. RR Hydraulic provides pull-out and pull-through test data in EC3 Part 1-3 format for structural engineer verification.
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 structural fastener supply. RR Hydraulic provides documentation in EN 10204 or ISO 10474 format as specified by the project purchase order or vendor qualification requirements.
ISO 4413
Safety requirements for hydraulic fluid power systems. Self-drilling screws used in HPU enclosure structural panels, skid base frame cladding, and hydraulic control room building structural cladding must comply with ISO 4413 cleanliness requirements. For HPU and hydraulic system enclosure cladding work, SS A4-70 self-drilling screws prevent rust contamination from screw corrosion in the vicinity of open hydraulic systems.
Submit your TEK class schedule, corrosion category, head type, material, coating, and quantity to RR Hydraulic for a complete, certified commercial offer.