ASTM A574 Alloy Steel Socket Head Cap Screws (170–180 ksi)
The socket head cap screw specification: alloy steel quenched and tempered to 180 ksi in ½ in. and smaller and 170 ksi above, 37 to 44 HRC, black oxide — the standard for tooling, machinery and die work.
What A574 is.
ASTM A574 covers alloy steel socket head cap screws in inch sizes: 180 ksi minimum tensile at ½ in. and smaller and 170 ksi above, with a 140 or 135 ksi proof load and a hardness of 37 to 44 HRC. The steel must be alloy, with 0.33 percent carbon minimum, and the screws are supplied bright or with a thermal or chemical black oxide finish unless a coating is ordered. Dimensions follow ASME B18.3.
We machine A574 socket head cap screws in the odd lengths, drilled heads and special threads that stock does not cover, from certified 4140 and 4340 bar, heat treated and black oxided.
Chemical composition.
| Element | Symbol | Min % | Max % |
|---|---|---|---|
| Carbon | C | 0.33 | — |
| Phosphorus | P | — | 0.035 |
| Sulfur | S | — | 0.040 |
| Alloying elements | — | required | — |
Values per ASTM A574-21 Table 2 (verified against the specification). Confirm the edition called out on your purchase order with our estimating team. Alloying elements per the alloy steel definition in 6.2.
Mechanical properties.
| Grade / condition and size | Tensile strength, min (ksi) | Yield or proof, min (ksi) | Elongation, min (%) | Reduction of area, min (%) | Hardness |
|---|---|---|---|---|---|
| ½ in. and smaller (full size) | 180 | 140 proof | — | — | 39–44 HRC |
| Over ½ to 1 in. (full size) | 170 | 135 proof | — | — | 37–44 HRC |
| 1 in. and larger (machined specimen) | 170 | 153 yield | 10 | 35 | 37–44 HRC |
Values per ASTM A574-21 Table 1 (verified against the specification). Confirm the edition called out on your purchase order with our estimating team.
Specifications that apply.
How A574 ships from Houston.
- Hex and heavy hex bolts and cap screws
- Studs and threaded rod
- Nuts and washers to match
- Machined specials to drawing
A574 fasteners we make.
Every item is manufactured to your drawing or standard in A574, imperial or metric, with an EN 10204 3.1 certificate.
What is A574?
A574 is the specification behind the black socket head cap screw. It demands alloy steel, a minimum carbon content that guarantees hardenability, and a hardness window of 37 to 44 HRC that gives 170 to 180 ksi tensile with enough toughness to survive a wrench. The proof load, 135 or 140 ksi, is the stress the screw must carry without permanent set. Metric socket head cap screws to ISO 4762 in Class 12.9 are the equivalent product.
Testing, certification and marking
- Tensile, proof load and hardness per lot to ASTM F606
- Manufacturer's identification on the head; no grade mark is required by the specification
- Certificate of conformance or test report with heat number
- Hydrogen embrittlement bake after any plating
ASTM F835 Alloy Steel Socket Button and Flat Head Cap Screws
The low-head socket screws: button and flat countersunk heads in alloy steel at 144 ksi (½ in. and smaller) and 136 ksi above, 37 to 44 HRC — rated below A574 because the shallow head, not the shank, limits the load.
ASTM F912 · ASME B18.3ASTM F912 Alloy Steel Socket Set Screws
The socket set screw specification: alloy steel through hardened to 45 to 53 HRC, torque tested rather than tensile tested, with cup, flat, cone, oval and half-dog points — black oxide finished.
ASTM F837-20 · ASME B18.3ASTM F837 Stainless Steel Socket Head Cap Screws
The stainless socket head cap screw specification: 304-group and 316-group alloys annealed or cold worked, or 410 hardened and tempered to 180 ksi, passivated and dimensioned to ASME B18.3 — the corrosion-resistant counterpart of A574.