How to Choose a #8 Screw Diameter
Wood screws are used in a variety of applications, from framing wall studs to attaching molding and building bookshelves. Choosing the right size screw depends on several factors, including the type of wood and the type of joint you’re making. For example, face joints, which bring together the top and bottom surfaces of two boards, are often stronger than end joints. Using a screw that is too thick for the job can cause the wood to split. To prevent this, DIYers typically pre-drill a hole in the wood to the proper screw diameter before inserting the screw. Screws identified as self-drilling, however, feature a sharp tip that mimics the action of a drill bit, eliminating the need to pre-drill.
The size of a screw is indicated by its gauge, threads per inch (or TPI), and shaft length in inches. You may also see these measurements separated by a hyphen, like 6-32 x 1 1/2″. This means that the screw has a #8 diameter, 32 threads per inch, and is an inch and a half long.
In addition to the screw’s narrow measurement, you will also find it marked with its tolerance class and head diameter. The latter indicates how tightly the screw will fit into a nut or threaded hole. You’ll usually see a number from 1 to 5, with sizes 1 and 2 fitting loosely and those in the higher numbers fitting more tightly. For some screws, the number will be followed by the letter A or B to indicate left-handed or countersunk heads.
If you’re working with hardwoods, it’s best to use a drill bit that is slightly smaller than the screw’s narrow measurement to prevent splitting and cracking the wood. If you’re working with softwoods, such as pine, it’s okay to use a bit that is closer to the screw’s narrow measurement.
When choosing a screw length, it’s important to consider the thickness of the boards you’re joining. The general rule of thumb is that the screw should enter the top board by about 1/2 of its thickness, meaning a 2×4 screw should go into a 2×4. If you’re working with extremely thick or heavy materials, though, you might need to use longer screws.
You’ll also need to decide if you want to use self-drilling or non-self-drilling screws. Self-drilling screws feature a sharp tip that creates a pilot hole as it enters the wood, eliminating the need to pre-drill holes for them. Non-self-drilling screws, on the other hand, have a flat, round tip that can’t penetrate wood as deeply as the head of the screw. This makes them better suited for use in thin or lightweight boards, such as trim and molding. If you’re not sure which type to choose, check out this handy guide from The Home Depot. It gives a good overview of the different types of wood screws available and their uses. The article also provides tips on how to measure the diameter of a screw. #8 screw diameter