Sheet metal screws and wood screws have much in common and one type can sometimes be used in place of the other. How are they alike and how do they differ? Read on to find out.
Sheet Metal Screw
A sheet metal screw is a self tapping screw that is typically used to secure sheet metal to metal, plastic, fiberglass, wood or other materials. It is also used to attach hinges, hasps, brackets and other types of hardware.
Because they are self tapping, sheet metal screws create their own mating threads. This enhances the screws holding power. Depending on the screws and the type of material, a pilot hole may or may not be required. A sheet metal screw is threaded along the entire shank further enhancing its ability to stay in place.
A wood screw is used to secure one piece of wood to another. It can also be used to attach hardware to wood as long as a pilot hole is drilled that can accommodate the unthreaded portion of the screw.
A wood screw has a tapered body and coarse threads with the upper portion of the shank unthreaded. The unthreaded portion improves the ability of the screw to pull mating pieces of wood together. A wood screw is specially tempered so that it will bend before breaking. This is an important characteristic because wood will shrink and expand over time due to seasonal variations in relative humidity.
A sheet metal screw can sometimes be used in place of a wood screw for attaching an object to a piece of wood. However, a wood screw is generally not a suitable replacement for a sheet metal screw because the threads are not designed to cut into metal and the unthreaded upper shank can be problematic.
There are several different types of sheet metal screws including button, flat, hex washer, oval, pan, round, and truss screws. The pan head screw, one of the most commonly used sheet metal screws, has a partially rounded head that protrudes above the surface.
There are also several different types of wood screws. The classic wood screw has a flat head that is countersunk to be flush with or below the wood surface. Two other commonly encountered wood screw types are the raised head screw and the roundhead screw. A raised head screw is countersunk with a slight dome head projecting above the surface. A roundhead wood screw rests on the surface.
Wood screws are typically sized so that approximately two thirds of the screw will protrude into the bottom piece to maximize holding power. A pilot hole is often required when installing a wood screw, a specially if the wood is very hard or susceptible to splitting.
The two-thirds rule doesn’t apply to sheet metal screws because the screws are generally threaded into harder materials like metal that are less likely to strip than wood. Or, the screws are attached to relatively thin material such as metal ducting so there is no advantage to having the screw protrude beyond the piece it is attached to.