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screw, simple machine consisting essentially of a solid cylinder, usually of metal, around which an inclined plane winds spirally, either clockwise or counterclockwise. It is used to fasten one object to another, to lift a heavy object, or to move an object by a precise amount. The ridge forming the inclined plane is called the thread; in cross section the ridge may be approximately triangular, square, or rounded. The vertical distance from any point on one thread to a corresponding point on the next successive thread is called the pitch. A thread can also be placed on the inner surface of a hollow cylinder. Two screws of the same pitch and diameter, one on the outer surface of a solid cylinder and the other on the inner surface of a hollow cylinder, can be arranged so that one may be driven spirally into the other, as in the common nut and bolt. The thread on the surface of the bolt is called the external, or male, screw; that on the inner surface of the nut, the internal, or female, screw. The common jackscrew used to lift automobiles, houses, and other heavy objects is an application of this principle. The internal screw is situated in the base, the external screw on a metal cylinder; at the top of the cylinder a lever or handle is fastened. As the handle is rotated, the external screw moves up the internal screw and the object placed on top of the jack is lifted. The mechanical advantage of the jackscrew, as of any other screw, is theoretically the ratio between the circumference through which the end of the handle moves and the pitch of the screw. Since, however, there is much friction in the operation of a screw, the amount of work put into this machine is much greater than the amount done and the efficiency is small. On the other hand, the small effort necessary to turn the handle, when compared to the enormous load raised, makes such a device of great value. The screw is often used for making delicate adjustments of tools and machines, e.g., in the micrometer screw and in the carburetor of the gasoline engine (for regulating the flow of gasoline). The self-tapping screw has notches in the first few threads that can cut female threads in a hollow cylinder. Wood and metal screws, the carpenter's and machinist's vise, the propeller of a boat or airplane, Archimedes' screw, and many other devices are applications of the screw.
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The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.



a machine part of cylindrical—sometimes conical—shape, with a helical surface; or a part with helical blades. Screws are grouped as follows: screws that interact directly with an external, or working, medium, and screws that interact with a threaded opening of another part. The first group includes screws used for the production of rotary motion from moving gases and liquids (for example, in a wind engine); for the production of a tractive force (for example, an airplane propeller or a screw propeller on a ship); and for moving gases, liquids, and viscous, friable, or lump materials, sometimes with the creation in them of pressure and agitation (for example, in fans, pumps, screw conveyors, screw presses, and stirring screw conveyors). The second group includes motion screws, heavy-duty (force) screws, micrometer screws, fastening screws, and set screws.

A motion screw is the basic part of the screw mechanism in lathes and machines used for the rectilinear movement of assemblies and components (supports, tables, and so on) along a set of guides. Motion screws generally have a trapezoidal thread shape—less frequently square, triangular, or special—for screwing on nuts.

A heavy-duty force screw is a main part of a screw mechanism designed to produce large axial stresses in presses, furnace pushers, jacks (load-lifting screws), and so on. Force screws generally have a trapezoidal or buttress thread, less frequently a square thread. Short force screws, such as those in jacks, work by compression; they are checked for strength and buckling during their design and manufacture. Long force screws work by tension and are tested for tensile strength.

Micrometer screws have a precision thread with a small pitch; they are used in measuring machines, devices, and instruments (for example, in micrometers).

A fastening screw is a basic part of a detachable screw joint; the body of the screw has a threaded shaft at one end and a head at the other end. Fastening screws for metals and other solid materials usually have a triangular cylindrical thread. Noncritical small-diameter (to 8 mm) fastening screws are also made as self-tapping screws, with a tapered portion of partially shaped thread on the point. This type of screw extrudes the thread (in soft metals) or cuts it (in plastics and hard metals) when screwed into a smooth hole. Wood screws, which are used for fastening wooden parts, have a tapered portion of the thread at the point. The screw head serves both as a clamp for the parts to be joined and as a grip for tightening the screw with a screwdriver, wrench, or other tool. Standard fastening screws with hexagonal, square, and other types of heads are widespread.

Setscrews are generally used for the precise clamping of geodetic and other types of instruments, as well as for fastening screws in screw joints. Setscrews differ in the shape of the head and the clamping (adjusting) point.


The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.

What does it mean when you dream about a screw?

The dreamer may feel as if they are being turned like a screw in a situation where someone is taking advantage of them.

The Dream Encyclopedia, Second Edition © 2009 Visible Ink Press®. All rights reserved.


(design engineering)
A cylindrical body with a helical groove cut into its surface.
A fastener with continuous ribs on a cylindrical or conical shank and a slotted, recessed, flat, or rounded head. Also known as screw fastener.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.


screw: nomenclature
An externally threaded fastener.
McGraw-Hill Dictionary of Architecture and Construction. Copyright © 2003 by McGraw-Hill Companies, Inc.


1. a device used for fastening materials together, consisting of a threaded and usually tapered shank that has a slotted head by which it may be rotated so as to cut its own thread as it bores through the material
2. a threaded cylindrical rod that engages with a similarly threaded cylindrical hole; bolt
3. a thread in a cylindrical hole corresponding with that on the bolt or screw with which it is designed to engage
4. Billiards snooker
a. a stroke in which the cue ball recoils or moves backward after striking the object ball, made by striking the cue ball below its centre
b. the motion resulting from this stroke
5. another name for propeller
6. Slang an old, unsound, or worthless horse
Collins Discovery Encyclopedia, 1st edition © HarperCollins Publishers 2005


(MIT) A lose, usually in software. Especially used for user-visible misbehaviour caused by a bug or misfeature. This use has become quite widespread outside MIT.
This article is provided by FOLDOC - Free Online Dictionary of Computing (