What Are Self Tapping Screws? The Complete UK Guide

Thread cutting self tapping screws have a sharp leading edge, often with a small notch or slot near the tip, that works rather like a tiny tap, shaving away a fine curl of material as the screw turns and physically cutting a matching thread groove. These are the choice for harder or thicker materials, such as sheet metal or dense timber, where the material needs to be removed rather than simply pushed aside.

Thread forming self tapping screws, sometimes called thread rolling screws, work differently. Instead of cutting material away, the screw's thread presses the surrounding material outward as it turns, moulding a thread shape without removing any material at all. This suits softer materials such as plastics and thin, softer metals, where a formed thread grips just as well and leaves no loose swarf behind to jam the fixing later.

The confusion mostly comes down to the tip of the screw. A self tapping screw has a sharp point but still needs a pilot hole drilled first in most materials, especially metal, so the thread has somewhere to cut into. A self drilling screw takes things a step further with a genuine drill-bit style point, letting it bore its own hole and then immediately cut its own thread in a single motion, with no separate drilling step at all. Self drilling screws are brilliant for fixing directly into metal purlins or thicker steel without a pilot hole, while self tapping screws are the more general purpose choice across a wider range of materials.

A standard wood screw is designed to work with the natural softness and grain of timber. Its coarse thread bites into the wood fibres, and in most cases it benefits from a pilot hole to prevent splitting, though timber is soft enough that the screw can often make some headway on its own. A self tapping screw, by contrast, is engineered with a harder point and a thread specifically shaped to cut a clean channel into firmer or less forgiving materials such as metal or plastic, where a standard wood screw would simply strip out or refuse to bite at all.

In practice, many general purpose self tapping screws will work perfectly well in timber too, which is part of why the terms get blurred. If you are working purely with wood, though, a dedicated wood screw with the right gauge and length for the job is usually the better and more cost-effective choice. You can browse our full range on the wood screws collection page.

Type A self tapping screws have a widely spaced, coarse thread and a sharp gimlet point, and are one of the most common general purpose self tapping screws around. They cut a thread as they are driven and suit thinner sheet metal, plastics, and softer materials where a coarser thread gives a stronger initial grip.

Type B screws have a finer, more closely spaced thread than Type A and a blunter point. They are typically used in thicker sheet metal, castings, and plastics, where the finer pitch cuts a neater thread and gives a more secure, vibration-resistant hold once fitted.

Type AB screws blend the sharper point of Type A with a thread pitch closer to Type B, giving a versatile screw that performs well across a wider range of sheet metal thicknesses and plastics. This is why Type AB has become one of the most widely stocked general purpose self tapping screws in trade merchants.

Types such as F, BT, and T feature a distinctive slot or fluted section at the tip, working much like a small tap and physically cutting away material rather than displacing it. These are used for fixing into harder materials including thicker steel, cast metals, and dense plastics, where a purely thread forming screw would not have enough bite.

Gauge describes the diameter of the screw, usually shown as a number such as No.6 or No.8, with a higher number meaning a thicker screw. Choose a gauge that suits the thickness and strength of the material and the load the fixing will carry, since too thin a gauge risks snapping under load while too thick a gauge can split thinner or more brittle materials.

Length should generally allow the screw to pass fully through the item being fixed and penetrate the base material by at least the diameter of the screw, ideally more where the base material allows. Head type matters for both function and finish: pan head and countersunk heads are the most common general purpose choices, with countersunk heads sitting flush for a neat finish, while pan heads sit proud and are often used where extra clamping surface is helpful.

Assuming self tapping means no pilot hole is needed is the most common error of all. Most self tapping screws, aside from dedicated self drilling types, still need a pre-drilled hole to give the thread somewhere to cut into. Skipping it risks a snapped screw, a stripped hole, or a fixing that never sits flush.

A pilot hole that is too small forces the screw to fight the material, risking a stripped or snapped fixing. One that is too large leaves the thread with nothing solid to bite into, so the screw spins freely without ever tightening. Always check the manufacturer's recommended pilot hole size for the specific screw gauge and material, rather than estimating by eye.

Fitting a thread forming screw into a material too hard for it to displace will simply stall the fixing or strip the drive head under the extra torque needed. Equally, a thread cutting screw with a slotted tip driven into a soft plastic can crack or shatter the material around the hole. Match the screw's mechanism, not just its size, to the material you are working with.

Using an uncoated or low-grade self tapping screw in an outdoor fixing, such as guttering brackets or external cladding, is a common way to end up with rust streaks and a loosening fixing within a season or two. Choose zinc-plated, galvanised, or stainless steel screws for anything exposed to the weather, and stainless as standard near the coast.