Socket Head Cap Screw

A socket head cap screw is a threaded fastener with a cylindrical head and a hexagonal recess. It is turned with an Allen key or hex bit.

A socket head cap screw clamps parts through a drilled and tapped hole or with a nut. It takes a hex key, also called an Allen key, and often a washer. It suits machine building, tooling and general engineering where a compact head is needed.

Black oxide gives a dark finish with light oil retention for indoor machinery. Zinc plating gives a bright, thin coating for mild indoor use. Hot-dip galvanising gives a thick coating for outdoor and wet areas.

This kind of screw is often made in steel, stainless steel 304, stainless steel 316, iron, copper, aluminium or titanium. Steel grades can be class 8.8, 10.9 or 12.9. Stainless steel 304 and 316 resist corrosion, with 316 better for salt and chemical exposure.

This is a general guide to checking this kind of part. It says nothing about any supplier's parts.

Ask for a mill test certificate or a certificate of conformance for the material and grade. On receipt, check the hex recess for damage, the thread form and the head dimensions. Confirm the screw threads into a matching nut or gauge without binding.