Most screws and bolts are tightened by clockwise rotation, which is called a right-hand thread. The distance between each thread is called the pitch. The cylindrical portion of the screw from the underside of the head to the tip is called the shank it may be fully or partially threaded. A J-bolt has a J-shaped head that is sunk into concrete to serve as an anchor bolt. A set screw may have a head the same size or smaller than the outer diameter of the screws thread a set screw without a head is sometimes called a grub screw.

A carriage bolt has a domed head that is not designed to be driven. The head is usually larger than the body of the screw, which keeps the screw from being driven deeper than the length of the screw and to provide a bearing surface. Common tools for driving screws include screwdrivers and wrenches. The most common uses of screws are to hold objects together and to position objects.Ī wood screw: a) head b) non-threaded shank c) threaded shank d) tip.Ī screw will usually have a head on one end that allows it to be turned with a tool. Other screw threads are designed to cut a helical groove in a softer material as the screw is inserted. 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. Screws and bolts are used to fasten materials by the engagement of the screw thread with a similar female thread (internal thread) in a matching part.

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).

Flat head stainless steel screws