![]() The document seems to have no significant effect on common usage and does not eliminate the ambiguous nature of the distinction between screws and bolts for some threaded fasteners. The federal government of the United States made an effort to formalize the difference between a bolt and a screw, because different tariffs apply to each. Some of these issues are discussed below: ![]() The issue of what is a screw and what is a bolt is not completely resolved with Machinery's Handbook distinction, however, because of confounding terms, the ambiguous nature of some parts of the distinction, and usage variations. This distinction is consistent with ASME B18.2.1 and some dictionary definitions for screw and bolt. (Example: round head bolts, track bolts, plow bolts.) An externally threaded fastener that has thread form which prohibits assembly with a nut having a straight thread of multiple pitch length is a screw. An externally threaded fastener which is prevented from being turned during assembly and which can be tightened or released only by torquing a nut is a bolt. A screw is an externally threaded fastener capable of being inserted into holes in assembled parts, of mating with a preformed internal thread or forming its own thread, and of being tightened or released by torquing the head. Machinery's Handbook describes the distinction as follows:Ī bolt is an externally threaded fastener designed for insertion through holes in assembled parts, and is normally intended to be tightened or released by torquing a nut. Part of the confusion over this is likely due to regional or dialectical differences. There is no universally accepted distinction between a screw and a bolt. ( March 2023) ( Learn how and when to remove this template message) You may improve this, discuss the issue on the talk page, or create a new, as appropriate. The examples and perspective in this deal primarily with the United States and do not represent a worldwide view of the subject. For this reason, the left-side pedal of a bicycle has a left-hand thread.ĭifferentiation between bolt and screw A carriage bolt with a square nut A structural bolt with a hex nut and washer Screws with a left-hand thread are used in exceptional cases, such as where the screw will be subject to counterclockwise torque, which would tend to loosen a right-hand screw. 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. 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).
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