Written by Jody Muelaner

Hex head screws are screws with a hexagonal-shaped head that can be tightened with a wrench (spanner) or socket. Such tools engage with the external faces of the hex head.

Avoid confusing hex head screws with a hexagon socket head or an Allen, which have an internal hexagonal socket that is driven by hex bits or keys. Hex heads always have an external hexagon head.

A screw is a mechanical fastener with a threaded shaft that screws directly into a part. The “hex head” term typically refers to a machine screw with a preformed machine thread. Machine screws resemble bolts but with a threaded shaft.

Less commonly, wood and self-tapping screws have a hex head, which is helpful when high torque is required. These types of screws have a tapered shaft with sharp threads, designed to cut a mating thread in the part to which they’re to be fastened.

Some hex head screws have a slotted or Philips head in conjunction with a standard hex head so that a screwdriver can be used, rather than a wrench or socket. These are referred to as a combi-screw.

Hex head screws may also have full-bearing, washer, or flanged heads with bonded washers. These fasteners are available in zinc-plated, galvanized, organic-coated, and stainless steel, as well as in bronze, nylon, or bi-metal.

The screws are designed to mate with a machine thread (also known as hex cap screws), setscrews, or machine screws, which secure an object within or against another object.

The American National Standard and Unified Standard Heavy Hex Screws and Hex Cap Screws ANSI/ASME B18.2.1-1996, specifies the hex head screws’ size range, which is 0.25–3 in (6.35–76.20 mm) in diameter.

Hex head screws that tap their own hole are also known as lag or coach screws. They’re used to join heavy timber or heavy objects with timber. They can also attach heavy objects to masonry or light objects to steel. These types of hex head screw have a tapered point that inserts into a pilot hole or nylon plug and a sharpened point that can pierce timber or light-gauge steel, or a gimlet point that’s for displacing timber.

Self-drilling hex head or Tek screws are used for joining metal to metal. They have a fluted tip that self-drills when driven, eliminating the need for a pilot hole. Self-drilling hex head screws have a drill point of varying lengths, depending on the thickness of the metal being fixed to.