Socket Head Cap Screws
Socket head cap screws have a round, cylindrical head with an internal hex drive. They give high strength in a small footprint. Three different material families use the same shape.
Three material families, same head shape
| Family | Standard | Strength | Typical marking |
|---|---|---|---|
| Inch alloy steel | ASTM A574 | 180 ksi min tensile to 1/2 in; 170 ksi above | Maker ID (often knurled head) |
| Metric alloy steel | ISO 4762 + ISO 898-1 | Class 12.9: 1220 MPa min | 12.9 plus maker ID |
| Stainless | ASTM F837 / ISO 3506 | A2-70: 700 MPa (much lower) | Alloy/class mark plus maker ID |
These tables carry the same figures as the printed sheet below.
The printed sheet
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Text version of this sheet
ASME B18.3 (inch) · ISO 4762 / DIN 912 (metric) · socket head cap screws
FIELD IDENTIFICATION
What it is
Socket head cap screws have a round, cylindrical head with an internal hex drive. They give high
strength in a small footprint. Three different material families use the same shape.
Cylindrical head, hex socket (Allen) drive
Three material families, same head shape
Family
Standard
Strength
Typical marking
Inch alloy steel
ASTM A574
180 ksi min tensile to 1/2 in; 170 ksi above
Maker ID (often knurled head)
Metric alloy steel
ISO 4762 + ISO 898-1
Class 12.9: 1220 MPa min
12.9 plus maker ID
Stainless
ASTM F837 / ISO 3506
A2-70: 700 MPa (much lower)
Alloy/class mark plus maker ID
Key points
A black finish does not mean alloy steel, and a silver finish does not mean stainless. Check the marking and paperwork.
Stainless socket screws are roughly half the strength of alloy ones. Never substitute stainless where alloy was specified.
Governing standards: ASME B18.3-2012; ASTM A574-21; ASTM F837-20; ISO 4762:2004; ISO 898-1:2013; ISO 3506-1/-2:2020. Editions shown are the latest confirmed as of
September 2026. The drawing and the governing standard always take precedence over this sheet.
torquing any fastener. Verify the current governing standard, project documents, OEM requirements, size, thread, coating and lot certification. To the fullest extent permitted by law, The Fastener App disclaims liability
arising from reliance on this reference.
Fastener Guide reference FG-321355 · thefastenerapp.com/fastener-guide/technical-reference/socket-head-cap-screws · © The Fastener App. Reference only — verify the current governing standard, drawing and manufacturer data before specifying or installing.
