Screws

Every screw here is an externally threaded machine screw: a straight shank with a machine thread the whole way, meant for a tapped hole or a nut. Nothing in this section is self-tapping and nothing is a wood screw. What separates the four families is the head, and the head is what you choose on.

Choosing a head

Socket head cap is the default when torque matters. The cylindrical head is small in diameter and the internal hex engages six flats, so it takes far more torque than any cross recess and works down a counterbore where no wrench would fit.

Button head trades torque for profile. The domed head sits low and rounded, which is what you want on an exposed surface or where something slides past. The socket is shallower than a cap screw’s, so it will round out sooner — seat the key fully.

Flat countersunk sits flush. It needs a matching countersunk hole and it centres itself in that cone, which also means it will pull a part sideways if the hole is off.

Pan head Phillips is the general-purpose fastener: driven with a screwdriver, no counterbore, no countersink. It is the cheapest to install and the weakest to drive, because a cross recess cams out by design.

Threads and sizes

Metric runs M1.6 through M6 in coarse pitch, imperial runs #4-40 and #6-32. Metric and imperial threads of similar diameter are never interchangeable — M3 and #4-40 differ in both pitch and major diameter, and forcing one into the other strips the softer part. Each listing states the nearest imperial equivalent and repeats that warning.

What is on every listing

Thread size and pitch, head and drive dimensions in millimetres and inches, the hex key or driver size, the tap drill for a threaded hole at 75% engagement, the ISO 273 medium clearance hole for a through hole, and the DIN and ISO standards the part is built to. Full tables are on the reference pages.

Material

Stainless steel 304 throughout: non-magnetic in the annealed condition, resistant to indoor and general atmospheric corrosion, not rated for prolonged salt water. Use 316 where chlorides are present.