Screw Sizes – What You Need to Know

Whether you’re an avid DIYer or a professional, it is important to understand screw sizes. There are many different types of screws designed for varying materials, including wood, metal, PVC and concrete, so choosing the right type for your project is crucial to ensure that it’s secure. Often, this is determined by the material thickness; for example, thicker materials may require longer fasteners to guarantee that they can take the strain.

Screws are also categorized by their head and drive type, with the most common being slotted, Phillips, square and quadrex drives. They can also be classified as countersunk or non-countersunk, with the former sitting below the surface of the material and the latter sitting above. Other defining characteristics include screw gauge, which refers to the diameter of the shank, and thread per inch, which dictates how many threads are in one inch of the screw.

Measuring screw size can be done with a ruler or measuring tape and a screw gauge guide, which is available from most hardware stores. Simply measure from the end of the screw’s shank to where its head rests if it’s a countersunk screw or, for round-headed screws, where the oval top rests on the surface of the material. You can then compare this to a gauge guide to determine the screw’s major diameter, or use a caliper to measure from the bottom cavity of the thread to the other side and find the minor diameter. pilot hole for 1/4 lag screw