Screws make for very strong fixings, thanks to the grip that their spiral threads exert in the material into which they're driven. They also allow you the luxury of being easy to remove if you want to dismantle an item you have assembled.

Parts of a screw

A screw consists of a head, a shank and the tapered thread:

The head contains a recess that allows you to drive the screw with a screwdriver.

The shank may be smooth or threaded, and its diameter gives the screw its size, denoted by a gauge number. Common sizes range from gauge numbers 4 to 12, but smaller and larger sizes are available.

The thread may be a single or double spiral, and can extend, in modern screws, right up to the head. The screw length is the measurement between its tip and the part of the head that fits flush with the work surface.

Most screws are made of mild steel, either plain or galvanised. Corrosion-resistant screws are made from brass and stainless steel, or from zinc-plated, sherardized or black japanned steel.

Woodscrews

This is the most common type of screw, and comes in gauges ranging from 2 to 18 and in a variety of finishes.

Heads may be countersunk (cone-shaped with a flat top), raised countersunk (with a curved top, used mainly for fixing metal or plastic items such as door and window fittings to wood) or round (sitting proud of the work surface, used for fixing thin sheet materials that are too thin to take a countersink). Countersunk screws may have slots or cross-shaped Pozidriv recesses, while other types usually have slotted heads.

Lengths range from 9 to 150mm

Chipboard Screws

Chipboard screws are made from hardened steel and come with a fully threaded shank and a cross-shaped head recess. They are designed to give a better grip than a traditional woodscrew when used in man-made boards.

Lengths range from 12 to 100mm.

Deck Screws

Deck screws have a cross-head and are specially designed for the fast fixing of timber decking, using a power screwdriver.

Lengths range from 50 to 75mm.

Drywall Screws

These special hardened cross-head screws are designed for use when fixing plasterboard to wooden or metal supports. The thread cuts its own pilot hole, and the head is countersunk.

Lengths range from 25 to 50mm.

Self-Tapping (Pan Head) Screws

Also known as Pan head screws they cut their own thread in metal, plastics and other thin sheet materials. Their pan heads are raised but flat-topped, and may have a slot or a cross-head recess.

Lengths range from 6 to 50mm.

Mirror (Dome Head) Screws

Mirror screws are countersunk screws with a slotted head that also contains a threaded hole into which a decorative plated dome is screwed to conceal the screw head.

Lengths are 25, 32 or 38mm.

Coach Screws

These heavy duty screws are ideal for assembling heavy framework. They have a square head that is driven by a spanner.

Lengths range from 50 to 150mm.

Screw Cups

The cups are brass or zinc-plated fittings sometimes used with countersunk screws to improve their clamping force, and to make the screw easier to withdraw if necessary.

The Flush and Surface-Mounted types are used to match screw gauge size numbers 6, 8 and 10.

Screw Caps / Covers

Caps are snap-on plastic covers designed to conceal screw heads once the screws have been driven. Some fit round the screw shank and have a snap-on cap; others are a simple push fit into screws with Pozidriv heads. They come in white, beige and dark brown.