Alloy Metric Socket Head Cap Screws

Metric alloy socket head cap screws conform to DIN 912 and ISO 4762 — the metric equivalents of the inch-series ASME B18.3 standard. Class 12.9 alloy steel provides a minimum tensile strength of 1,220 MPa (~177,000 PSI), making it the highest-strength standard metric cap screw in production use and the correct specification for precision machinery, mold and die tooling, hydraulic components, and European-designed OEM equipment. Eugene Fastener stocks metric alloy socket head cap screws in Class 12.9 from M2 through M24 from stock in Eugene, Oregon.

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Metric Alloy Socket Head Cap Screws — DIN 912, Class 12.9 and Class 10.9

Shop Metric Alloy Socket Head Cap Screws

Metric socket head cap screws conform to DIN 912 (also referenced as ISO 4762), which governs the dimensions, tolerances, and mechanical requirements for metric cylindrical-head hex socket cap screws. They are manufactured in Class 12.9 and Class 10.9 alloy steel. Class 12.9 is the standard for precision machinery and is the most widely used metric SHCS specification; Class 10.9 is used where slightly lower strength is acceptable. The compact cylindrical head and internal hex socket drive are dimensionally identical to inch-series SHCS in concept, but metric versions use ISO thread forms and metric hex key sizes.

Class 12.9 vs. Class 10.9

Class 12.9 is the highest standard property class for metric alloy fasteners. Minimum tensile strength: 1,220 MPa (~177,000 PSI). Minimum yield strength: 1,100 MPa (~160,000 PSI). Hardness: 39–44 HRC. Class 12.9 is the default specification for precision machinery, mold and die sets, hydraulic manifolds, and OEM equipment designed to metric standards. It exceeds the tensile strength of inch-series Grade 8 hex bolts (150,000 PSI) and matches or exceeds alloy ASTM A574 SHCS.

Class 10.9 provides 1,040 MPa (~151,000 PSI) minimum tensile strength — comparable to SAE Grade 8. Used in structural bolting applications, automotive, and wherever slightly lower strength is acceptable at potential cost savings. For precision machine building, specify Class 12.9.

DIN 912 vs. ISO 4762

DIN 912 is the German standard; ISO 4762 is the international standard. For practical purposes, they specify the same fastener and the terms are used interchangeably in engineering drawings and procurement. Both use the same dimensions, tolerance classes, and thread specifications. A fastener marked DIN 912 and one marked ISO 4762 of the same size and property class are interchangeable.

Hex Key Reference — Metric SHCS

Metric SHCS use larger hex keys than metric set screws of the same thread size. Common metric pairings: M3 uses 2.5mm; M4 uses 3mm; M5 uses 4mm; M6 uses 5mm; M8 uses 6mm; M10 uses 8mm; M12 uses 10mm; M16 uses 14mm; M20 uses 17mm. Using an undersized key risks rounding the socket — always verify.

Frequently Asked Questions

What is the tensile strength of Class 12.9 metric socket head cap screws?
Class 12.9 metric socket head cap screws have a minimum tensile strength of 1,220 MPa, approximately 177,000 PSI. This is the highest standard property class for metric alloy fasteners and exceeds SAE Grade 8 hex bolts (150,000 PSI) and is comparable to ASTM A574 alloy inch-series SHCS (170,000–180,000 PSI).

What is the difference between DIN 912 and ISO 4762?
For practical purposes, none. DIN 912 is the German standard and ISO 4762 is the international standard for metric cylindrical-head hex socket cap screws. They specify the same dimensions and thread forms and are used interchangeably on engineering drawings. A fastener conforming to DIN 912 meets ISO 4762 requirements of the same size and class.

Should I specify Class 12.9 or Class 10.9 metric SHCS?
Specify Class 12.9 for precision machinery, tooling, mold and die sets, and OEM mechanical assemblies — it provides 1,220 MPa vs. 1,040 MPa for Class 10.9. Class 10.9 is appropriate for structural applications where slightly lower strength is acceptable. When in doubt, Class 12.9 is the standard for machine building.

What hex key do metric socket head cap screws use?
Common metric pairings: M4 uses 3mm, M5 uses 4mm, M6 uses 5mm, M8 uses 6mm, M10 uses 8mm, M12 uses 10mm. These are larger than the hex keys used for metric set screws of the same thread size. Always verify — using an undersized key will round the socket.

Metric alloy socket head cap screws are the backbone of metric mechanical assemblies, used alongside metric flat washers and hardened washers for clamp load distribution, metric lock washers and prevailing torque nuts for vibration resistance, and metric dowel pins for close-tolerance location. For metric assemblies in corrosive environments, see stainless metric socket head cap screws (DIN 912, A2-70 or A4-70). For inch-series high-strength applications, see alloy steel socket head cap screws (ASTM A574). The full socket head cap screw selection and all socket fastener types are available through the Socket Head Cap Screws and Sockets categories.

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