Some screw threads are designed to mate with a complementary thread, called a female thread (internal thread), often in the form of a nut object with an internal thread. There are many screws for a variety of materials materials commonly fastened by screws include wood, sheet metal, and plastic.Ī screw is a combination of simple machines: it is, in essence, an inclined plane wrapped around a central shaft, but the inclined plane (thread) also comes to a sharp edge around the outside, which acts as a wedge as it pushes into the fastened material, and the shaft and helix also form a wedge at the point.
Screws are often self-threading (also known as self-tapping) where the thread cuts into the material when the screw is turned, creating an internal thread that helps pull fastened materials together and prevents pull-out. An assortment of screws, and a US quarter for size comparison A screw in macro view A bolt (with a nut) and a screwĪ screw and a bolt (see Differentiation between bolt and screw below) are similar types of fastener typically made of metal and characterized by a helical ridge, called a male thread (external thread). For other uses, see Screw (disambiguation). For the screw as a mechanism, see Screw (simple machine).
