Screw

1. a mechanical device for fixing one object to another, characterized by a spiral ridge cut on the external surface of a cylindrical rod of decreasing diameter towards its point. This is a male screw. In a female screw the screw is cut on the inside of a cylindrical cavity.
2. a colloquial term for a worn out or inferior horse.

• AISF bone s. — see buttress thread bone screw.
• buttress thread bone s. — the thread is not a simple V as in the standard thread but has one side of the groove at right angles to the direction of the screw and the other side at a 45° angle. Called also AISF, Howmett compression, Richards–Bechtol.
• cancellous bone s. — has a coarse thread; threaded to only the first third of the length of the screw.
• cortical s. — threaded the full length of the screw; fine thread to hold in dense bone.
• Howmett compression bone s. — see buttress thread bone screw.
• lag bone s. — used as a compressing unit between two fragments with the first half of the screw near the point threaded, with the diameter of the ridges greater than that of the unthreaded half near the head. As the ridged part of the screw bites in the walls of the drill hole in the distal fragment, the unthreaded part is free to move within the drill hole in the proximal fragment, thus compressing the two pieces of bone together.
• Richards–Bechtol bone s. — see buttress thread bone screw (above).
• standard bone s. — with a V thread the full length of the screw, with a single slot, cruciate or Phillips head.
• transfixation s. — orthopedic screw used to reattach bone fragments to a solid skeletal part. The proximal part near the head is not threaded and needs to be of a smaller diameter than the threaded portion nearer the tip.

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A screw is one of the six simple machines. All screws are helical inclined planes. A screw can convert a rotational force (torque) to a linear force and vice versa. The ratio of threading determines the mechanical advantage of the machine. More threading increases the mechanical advantage. A rough comparison of mechanical advantage can be done by taking the circumference of the shaft of the screw and divide by the distance between the threads.

A screw is a shaft with a helical groove or thread formed on its surface and provision at one end to turn the screw. Its main uses are as a threaded fastener used to hold objects together, and as a simple machine used to translate torque into linear force. It can also be defined as an inclined plane wrapped around a shaft.

Screws come in a variety of shapes and sizes for different purposes.

Thread as found on a screw.

Examples

• Lead screws and ball screws are specialized screws for translating rotational to linear motion.
• Automated garage doors, where a motor drives a long finely threaded shaft at relatively fast speed and lifts the heavy door at a slower rate.
• Archimedes' screw and worm gears are examples of this machine.
• Other real-world examples include: fan, jar lid, cork screw, drill bit, bolt and nut, and spiral staircase

See also

• Screw - the threaded fastener
• Archimedes' screw

v • d • e Simple machine Classical simple machines Inclined plane · Lever · Pulley · Screw · Wedge · Wheel and axle

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