Socket
Head Cap
Screws
Cylindrical-head Allen drive fastener in Grade 10.9, 12.9 high tensile and SS 304 / 316. Manufactured to DIN 912 · ISO 4762 · IS 2269. Metric M3–M24 and BSW 3/16"–5/8" in ready stock from Bengaluru.
Grade
10.9 · 12.9 · SS 304 · SS 316
Standard
DIN 912 · ISO 4762 · IS 2269
Size Range
M3 – M24 · BSW 3/16" – 5/8"
What is a Socket Head Cap Screw?
A socket head cap screw — commonly called an Allen bolt or Allen cap screw — is a precision fastener with a cylindrical head driven by an internal hexagonal socket. The head can be recessed flush into a counterbored hole, giving a clean, flush surface finish. The deep socket engagement allows significantly higher torque than external-drive hex bolts of the same diameter, without the risk of wrench slippage.
RM Traders stocks socket head cap screws in Grade 10.9 and Grade 12.9 High tensile for high-load structural and machine applications, and in SS 304 / SS 316 for corrosion-critical environments. Metric sizes run M3 to M24; and BSW imperial sizes are available.
High Tensile
Grade 10.9
Min tensile strength 1040 MPa. General high-tensile machine, structural and fixture applications. Alloy steel per ISO 898-1.
High Tensile
Grade 12.9
Min tensile strength 1220 MPa. Maximum strength grade — die & mould, engine assemblies, precision bores. Alloy steel per IS 1367.
Corrosion Resistant
SS 304 / 316
Austenitic stainless. SS 316 adds molybdenum for chloride/marine resistance. Metric + BSW range. SS 316L on enquiry.
Standards & Specifications
- DIN 912 / ISO 4762Primary standard for socket head cap screws. Identical dimensions and tolerances; fully interchangeable. Product Grade A per ISO 4759-1.
- IS 2269Bureau of Indian Standards equivalent. Specifies property classes 8.8, 10.9 and 12.9 per IS 1367. Threads per IS 4218 / ISO 261.
- ISO 898-1 / IS 1367Mechanical properties for property class 10.9 and 12.9. Grade 12.9 hardness: 39–44 HRC. Grade 10.9 hardness: 33–39 HRC.
Dimensional
Tolerances
Per DIN 912 / ISO 4762 — Product Grade A (ISO 4759-1). All dimensions in mm.
| d | p (mm) | Head dia dk (mm) | Head height k (mm) | A/F — s (mm) | e min (mm) | |||
|---|---|---|---|---|---|---|---|---|
| min | max | min | max | nom | min | |||
| M3 | 0.50 | 5.32 | 5.68 | 2.86 | 3.00 | 2.5 | 2.52 | 2.87 |
| M4 | 0.70 | 6.78 | 7.22 | 3.82 | 4.00 | 3 | 3.02 | 3.44 |
| M5 | 0.80 | 8.28 | 8.72 | 4.82 | 5.00 | 4 | 4.02 | 4.58 |
| M6 | 1.00 | 9.78 | 10.22 | 5.70 | 6.00 | 5 | 5.02 | 5.72 |
| M8 | 1.25 | 12.73 | 13.27 | 7.64 | 8.00 | 6 | 6.02 | 6.86 |
| M10 | 1.50 | 15.73 | 16.27 | 9.64 | 10.00 | 8 | 8.03 | 9.15 |
| M12 | 1.75 | 17.73 | 18.27 | 11.57 | 12.00 | 10 | 10.03 | 11.43 |
| M14 | 2.00 | 20.67 | 21.33 | 13.57 | 14.00 | 12 | 12.03 | 13.72 |
| M16 | 2.00 | 23.67 | 24.33 | 15.57 | 16.00 | 14 | 14.03 | 15.99 |
| M20 | 2.50 | 29.67 | 30.33 | 19.48 | 20.00 | 17 | 17.05 | 19.44 |
| M24 | 3.00 | 35.61 | 36.39 | 23.48 | 24.00 | 19 | 19.07 | 21.73 |
dk = head diameter · k = head height · s = across flat (A/F) hex socket size · e = across corners of socket · p = thread pitch
Sizes Available
Standard stocked metric range in High tensile and SS grades. BSW imperial sizes available in SS. Sizes outside these ranges on enquiry with MOQ.
HT Grade 10.9 & 12.9 — Metric (M3 – M16)
| Diameter | Length Range (mm) |
|---|---|
| M3 | 6 – 50 |
| M4 | 6 – 100 |
| M5 | 8 – 100 |
| M6 | 10 – 150 |
| M8 | 12 – 150 |
| M10 | 16 – 150 |
| M12 | 20 – 150 |
| M14 | 25 – 150 |
| M16 | 25 – 150 |
SS 304 & SS 316 — Metric (M3 – M24)
| Diameter | Length Range (mm) |
|---|---|
| M3 | 6 – 45 |
| M4 | 6 – 100 |
| M5 | 6 – 100 |
| M6 | 6 – 100 |
| M8 | 6 – 100 |
| M10 | 16 – 100 |
| M12 | 20 – 100 |
| M16 | 25 – 100 |
| M20 | 25 – 100 |
| M24 | 50 – 100 |
BSW Imperial Sizes — SS 304 & SS 316 Only
| BSW Size | Available Lengths |
|---|---|
| 3/16" | 1/4" – 1-1/4" |
| 1/4" | 1/4" – 3" |
| 5/16" | 1/4" – 3-1/2" |
| 3/8" | 1" – 4" |
| 1/2" | 1-1/2" – 4" |
| 5/8" | 3-1/2" – 4" |
SS 316L available on special enquiry — same diameter range as SS 316, lead time 7–14 days. Plating (zinc, BZP, nickel) available on HT grades on request — electroplating on Grade 12.9 requires post-plate de-embrittlement bake per ISO 4042; mechanical plating (Dacromet / Geomet) recommended as a hydrogen-free alternative.
Applications
CNC Machine Tools
Grade 12.9 socket screws are standard fasteners for tool holders, spindle housings and machine guarding where high clamping force and flush-head assembly are required.
Robotics & Automation
Used to assemble robot arms, servo mounts and linear rail brackets — the compact cylindrical head allows tight-pitch bolt patterns in confined aluminium extrusion frames.
Hydraulic Manifolds
High-pressure manifold blocks specify Grade 12.9 socket screws for port covers and sub-plate mounting, where high preload and precise torque are critical to joint integrity.
Die & Mould Tooling
Socket cap screws assemble mould plates, inserts and ejector housings. Grade 12.9 prevents the loosening caused by thermal cycling and repeated press loads.
Medical & Clean Room Equipment
SS 316 socket head cap screws are specified for surgical equipment frames, autoclave assemblies and pharmaceutical processing lines where passivation and hygiene are mandatory.
Precision Jigs & Fixtures
Inspection fixtures, welding jigs and CMM tooling use socket cap screws for repeatable clamping with counterbored, flush-surface assemblies that avoid interference with workpieces.
Frequently Asked
Questions
What is a socket head cap screw?
A socket head cap screw (also called an Allen bolt) is a cylindrical-head fastener driven by an internal hexagonal socket. Manufactured to DIN 912 / ISO 4762 / IS 2269, the compact head allows recessing into counterbored holes and high torque application in confined spaces. The deep socket drive prevents wrench slippage — making it the preferred fastener in CNC machine tools, hydraulic manifolds, precision jigs and die & mould tooling.
What is the difference between Grade 10.9 and Grade 12.9 socket head cap screws?
Grade 10.9 has a minimum tensile strength of 1040 MPa (proof load 940 MPa) and suits most high-tensile machine and structural applications. Grade 12.9 is the highest commercially available property class at 1220 MPa tensile (proof load 1100 MPa) — approximately 18% stronger than 10.9. Grade 12.9 is specified where maximum clamping force in minimum bolt diameter is critical: engine assemblies, die & mould tooling, precision fixtures. Both use chromium-molybdenum or boron alloy steel conforming to ISO 898-1 / IS 1367.
Can Grade 12.9 socket head cap screws be electroplated?
Electroplating Grade 12.9 carries a serious risk of hydrogen embrittlement. Hydrogen ions generated during acid pickling and electroplating diffuse into the high-strength steel lattice, causing delayed brittle fracture — sometimes hours after assembly. ISO 4042 mandates a post-plating de-embrittlement bake at 200–230°C for a minimum of 8 hours within 4 hours of plating. However, many engineers and specifications prohibit electroplating 12.9 entirely. The standard finish for Grade 12.9 is Black Oxide — mild corrosion resistance, no hydrogen risk. If a zinc coating is required, specify mechanical zinc plating (Dacromet / Geomet / Magni) — these are hydrogen-free and safe on 12.9 grade.
What is the difference between DIN 912 and ISO 4762?
DIN 912 is the German standard; ISO 4762 is the international equivalent that superseded it. Both specify identical dimensions and tolerances — a DIN 912 and ISO 4762 screw of the same size are fully interchangeable. In India, IS 2269 is the Bureau of Indian Standards equivalent. All three refer to Product Grade A dimensions per ISO 4759-1 and the same thread tolerance class 4g.
What Allen key size fits each socket head cap screw diameter?
Hex socket (s) sizes per DIN 912 / ISO 4762: M3 = 2.5 mm · M4 = 3 mm · M5 = 4 mm · M6 = 5 mm · M8 = 6 mm · M10 = 8 mm · M12 = 10 mm · M14 = 12 mm · M16 = 14 mm · M20 = 17 mm · M24 = 19 mm. Always use a quality Allen key — a worn key can round the socket and make removal very difficult, especially on Grade 12.9.
What tensile strength does a Grade 12.9 socket head cap screw have?
Per ISO 898-1 and IS 1367: Minimum tensile strength (Rm) = 1220 MPa, Proof load stress = 1100 MPa, Minimum yield strength (Rp0.2) = 1100 MPa, Hardness = 39–44 HRC. The "12.9" designation encodes the properties — "12" represents 1/100th of the nominal tensile strength (1200 MPa reference), "9" represents 90% yield-to-tensile ratio.
Are socket head cap screws available in stainless steel?
Yes. RM Traders stocks socket head cap screws in SS 304 (A2) and SS 316 (A3) in metric M3–M24 and BSW 3/16"–5/8". SS 304 suits general indoor and mild outdoor environments. SS 316 adds molybdenum for superior chloride and marine resistance. SS 316L (low carbon, for welded assemblies) is available on special enquiry. Note: stainless grades are rated A2-70 / A4-80 (700–800 MPa tensile) — significantly lower than Grade 12.9 alloy steel.
What is the recommended tightening torque for socket head cap screws?
Indicative values for Grade 12.9 (lubricated, μ = 0.12): M4 = 4 Nm · M5 = 8 Nm · M6 = 14 Nm · M8 = 34 Nm · M10 = 68 Nm · M12 = 118 Nm · M16 = 292 Nm · M20 = 580 Nm. For Grade 10.9 reduce by ~15%. For SS 304/316 reduce by 40–50%. Dry (unlubricated) conditions increase friction and may require 20–25% higher torque for the same preload. Always verify against the joint designer's calculations per VDI 2230.
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