Screw

A screw is a type of threaded fastener designed to hold materials together by being turned into a predrilled hole, a tapped hole, or directly into the material itself. Screws come in many forms, including machine screws (used with tapped holes or nuts), sheet metal screws (that form or cut threads in thin metal), and wood screws (designed to bite into wood fibers). When tightened, a screw develops clamp load that pulls parts together, helping the joint resist movement and loosening.

Screws are specified by their thread size and pitch (or threads per inch), length, head style (such as pan, flat, or truss), and drive type (such as Phillips, Torx, or slotted), as well as material and finish for corrosion protection. Choosing the right screw depends on what it’s fastening and how it will be installed, including whether the material needs a thread-forming design, whether the head must sit flush, and whether the joint will see vibration or outdoor exposure. Using the proper screw type and installation torque helps prevent issues like stripped threads, snapped fasteners, or inadequate clamping force.