Understanding Bolts and Screws

BOLT – A fastener consisting of a threaded pin or rod with a head at one end, designed to be inserted through holes in assembled parts and secured by a mated nut that is tightened by applying torque.

SCREW – A metal pin with incised threads and a broad slotted head that can be driven as a fastener by turning with a screwdriver, especially: a. A tapered and pointed wood screw. b. A cylindrical and flat-tipped machine screw.

BOLT – A metal rod or pin for fastening objects together that usually has a head at one end and a screw thread at the other and is secured by a nut.

SCREW – A nail-shaped or rod-shaped piece with a spiral groove and a slotted or recessed head designed to be inserted into material by rotating (as with a screwdriver ) and used for fastening pieces of solid material together.

BOLT – A strong pin, of iron or other material, used to fasten or hold something in place, often having a head at one end and screw thread cut upon the other end.

SCREW – Specifically, a kind of nail with a spiral thread and a head with a nick to receive the end of the screwdriver. Screws are much used to hold together pieces of wood or to fasten something. Webster's Revised Unabridged Dictionary

BOLT – A screw that screws into a nut to form a fastener.

SCREW – A fastener with a tapered threaded shank and a slotted head.

BOLT is a type of fastener formed of a metal rod that has an enlarged head at one end and a screw thread at the other. Bolts may be screwed directly into a threaded hole in the part they are to hold, or they may be held in place by nuts. A nut is a block of metal with a hole in the center. The hole is threaded to match the threads on the bolt.

SCREW is an inclined plane wrapped in a spiral around a shaft. The screw is one of the six simple machines developed in ancient times. The other five are the lever, the wheel and axle, the pulley, the inclined plane, and the wedge.

A screw consists of two main parts—the body and the thread. The body of a screw may be a cone or a cylinder. The center line of the body is called the axis. The thread is the inclined plane that sticks out from the body. The distance between two adjacent (neighboring) crests of the thread is known as the pitch.

Uses. Screws have many practical applications, especially as fasteners. The most common are the wood screw and machine screw. When rotated, such screws can be made to move into, or out of, an object. As the screw rotates one full turn, it travels a distance equal to its pitch. Most wood screws and machine screws have a slotted or recessed head into which a screwdriver is placed in order to turn the screw. Screws come in various sizes and shapes. They are made of steel, copper, aluminum, and other metals that are easy to form.

BOLT – A cylindrical fastener with an integral head on one end and an external screw thread on the other end designed to be inserted through holes in assembled parts and to mate with an internally threaded block, called a nut, which is turned to tighten or loosen the bolt. Tensioning the fastener by turning the nut differentiates a bolt from a screw, which is tightened by turning its head.

SCREW FASTENER – A threaded machine part used to join parts of a machine or structure. Screw fasteners are used when a connection that can be disassembled and reconnected and that must resist tension and shear is required. A nut and bolt is a common screw fastener.

The bolt is described as an externally threaded fastener designed for insertion through holes in assembled parts. It is normally tightened and released by turning a mating nut. A screw differs from a bolt in that it is supposed to mate with a[n] internal thread into which it is tightened or released by turning its head.

Differentiation between Bolt and Screw. – A 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.

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.

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. (Example: round head bolts, track bolts, plow bolts.)

An externally threaded fastener that has a thread form which prohibits assembly with a nut having a straight thread of multiple pitch length is a screw. (Example: wood screws, tapping screws.)

2.1 Bolt. A 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.

2.2 Screw. 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.

3. Explanatory Data. A bolt is designed for assembly with a nut. A screw has features in its design which makes it capable of being used in a tapped or other preformed hole in the work. Because of basic design, it is possible to use certain types of screws in combination with a nut. Any externally threaded fastener which has a majority of the design characteristics which assist its proper use in a tapped or other preformed hole is a screw, regardless of how it is used in its service application.

A bolt is a fastener that has external threads (a nut, for example, has internal threads), is inserted into an unthreaded hole of one or more parts, and is tightened or loosened by turning its nut. Carriage bolts, elevator bolts and plow bolts, for example, are bolts because you can't turn their heads to tighten or loosen them.

A screw has external threads just like a bolt. But a screw is inserted into a threaded or unthreaded hole, and is tightened or loosened by turning its head. It may or may not be used with a nut. Wood screws and sheet metal screws make their own threads in the hole, so they are not used with a nut. Machine screws and cap screws, for instance, thread into threaded holes or are used with a nut. In either case, though, you tighten or loosen the screw by turning its head.