1/4"-28 UNF 12.9 Socket Cap Bolts BS 2470

Product Description

1/4"-28 UNF ASTM A574 high-strength alloy steel socket cap head bolts with a part-threaded shank, available in lengths from 1 1/2" to 4 1/2".

These imperial Allen key bolts combine a cylindrical socket cap head with a fine-pitch Unified thread and a plain unthreaded shank. Manufactured from quenched-and-tempered alloy steel to ASTM A574, they are designed for demanding machinery, automotive, tooling and general engineering applications requiring high tensile strength.

• Thread size: 1/4"-28 UNF
• Threads per inch: 28 TPI
• Thread series: UNF – Unified National Fine
• Threading: Part threaded with an unthreaded shank
• Available lengths: 1 1/2" to 4 1/2"
• Head style: Cylindrical socket cap head
• Drive type: Internal hexagon / Allen key
• Nominal Allen key size: 3/16"
• Nominal head diameter: Approximately 0.375" / 9.53mm
• Nominal head height: Approximately 0.250" / 6.35mm
• Material: Quenched-and-tempered alloy steel
• Mechanical specification: ASTM A574
• Approximate metric strength comparison: Property class 12.9
• Finish: Self colour / unplated
• British dimensional reference: BS 2470 pattern
• Modern dimensional reference: ASME B18.3
• Pack sizes available: 1, 5, 10, 20, 50 and 100

These 1/4"-28 UNF socket cap bolts are suitable for machinery, automotive assemblies, motorsport, restoration projects, tooling, fabrication and general engineering applications requiring a long, high-strength imperial fastener with a plain shank.

ASTM A574 specifies quenched-and-tempered alloy steel socket head cap screws for applications requiring high strength. For this diameter range, ASTM A574 is commonly regarded as the closest imperial mechanical equivalent to metric property class 12.9.

The 28 TPI Unified National Fine thread has a finer pitch than the equivalent 1/4"-20 UNC thread. Fine threads provide greater thread engagement per unit of length and allow finer adjustment of clamping force. The mating nut or tapped component must have the correct 1/4"-28 UNF thread.

The part-threaded construction includes a plain unthreaded shank beneath the head. This allows the smooth shank to pass through supported components while the threaded end engages with a compatible nut or tapped hole. The exact thread length may vary according to the overall bolt length and manufacturing requirements.

The internal hexagon drive allows high tightening torque to be applied where external access around the head is restricted. Use a good-quality 3/16" Allen key or hex socket bit fully inserted into the recess to reduce the risk of rounding or damaging the drive.

Self-colour alloy steel is supplied without a zinc-plated or stainless protective finish. A light protective oil may be present, but additional corrosion protection should be applied where the fasteners will be exposed to damp, outdoor or chemically aggressive environments.

Socket cap bolt length is measured from directly beneath the head to the end of the bolt. The cylindrical cap head is not included in the stated length.

Please note: ASTM A574 is the confirmed material and mechanical-property specification for these high-strength alloy steel socket head cap screws. BS 2470 is retained as a British dimensional reference for the traditional imperial socket-cap pattern, while ASME B18.3 is the principal modern dimensional reference for inch-series socket screws. Nominal dimensions are provided as a guide and should be checked where fit, clearance or mechanical performance is critical.