Machine Screws

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Machine screws are small, fully threaded screws that go into a tapped hole or a nut. They hold electrical boxes, panels, hinges, brackets, guards and light assemblies together. This section covers number sizes such as 4-40, 6-32, 8-32 and 10-24 through 1/4" and larger, plus metric sizes. Head styles include pan, flat, oval, round, truss, fillister and hex washer, with Phillips, slotted, combination, square and six-lobe drives.

What to check before you order

  • Size and thread count. In a callout like 10-24, the first number is the gauge diameter and the second is threads per inch. 10-24 and 10-32 are both common, so check the hole before you buy.
  • Head style. Pan heads are the general choice. Flat heads need a countersunk hole. Truss heads have a wide, low head for thin sheet and slotted holes.
  • Drive. Square and six-lobe drives resist cam-out on power drivers better than Phillips or slotted.
  • Material and finish. Zinc-plated steel is standard for indoor use. Stainless steel and brass suit damp areas and electrical work where corrosion matters.

Common questions

What is the difference between a machine screw and a sheet metal screw?

A machine screw has a blunt end and uniform machine threads made for a nut or tapped hole. A sheet metal screw has a sharp point and coarse threads that form their own path.

Find matching hex and lock nuts, compare socket head screws, or return to fasteners.

Machine Screws: page 23

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