Socket Head Cap Screws

The cylindrical head with an internal hex drive, to ISO 4762 and DIN 912. The head is the smallest that will carry the full strength of the shank, which is why it is the standard fastener wherever a bolt has to sit in a counterbore or against a tight shoulder.

Why the socket drive matters

An internal hex takes far more torque than a slot or a cross recess of the same head diameter, and the key engages six flats instead of two. It also drives from directly above, so it works in a bore where no wrench would fit. The trade-off is that a rounded socket cannot be gripped by anything — use the correct key size and seat it fully.

Sizing the hole

Each listing carries the tap drill for a threaded hole at 75% engagement and the ISO 273 medium clearance hole for a through hole, in both millimetres and inches. The full tables are on the tap drill chart.

Material

These are 304 stainless: non-magnetic in the annealed condition, resistant to indoor and general atmospheric corrosion, but not the right choice against salt spray or chlorides — that is 316. Stainless galls readily against stainless, so on a joint you expect to open again, use an anti-seize compound.

For the equivalent standards in the ASME system, see the standards cross-reference.

Shop by thread size

Each size has its own page with the tap drill, clearance hole and hex key for that thread: M1.6, M2, M2.5, M3, M4, M5.