Single Screwdrivers

A screw is a shaft with a helical groove or thread formed on its surface. 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. more...

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Threaded fastener

A screw used as a threaded fastener consists of a shaft, which may be cylindrical or conical, and a head. The shaft has a helical ridge or thread formed on it. The thread is essentially an inclined plane wrapped around a shaft. The thread mates with a complementary helix in the material. The material may be manufactured with the mating helix (taps and dies), or the screw may create it when first driven in (a self-tapping screw). The head is specially shaped to allow a screwdriver or wrench (UK: spanner) to grip the screw when driving it in. It also stops the screw from passing right through the material being fastened and provides compression.

Screws can normally be removed and reinserted without reducing their effectiveness. They have greater holding power than nails and permit disassembly and reuse.

A screw that is tightened by turning it clockwise is said to have a right-hand thread. Screws with left-hand threads are used in exceptional cases, when the screw is subject to anticlockwise forces that might undo a right-hand thread. Examples include rotating items such as the left hand grinding wheel on a bench grinder or the left hand pedal on a bicycle (both looking towards the equipment).

Threaded fasteners are traditionally made by a cutting action such as taps and dies provide, however recent advances in tooling allows them to be made by rolling the blank (a section of rod) between two specially machined dies. The thread form and shape of the fastener are squeezed onto the blank. This method work hardens the threads and saves material. A rolled thread is obvious after manufacture because the outside diameter of the thread is greater than the diameter of the blank material. Bicycle spokes, which are just very long thin bolts, always use rolled threads for strength.

Bolt

A bolt is a cylindrical (as opposed to conical) threaded fastener that passes through the work piece and is held in place by a nut or a threaded hole on the other side. This is a very common way of holding together temporary and permanent constructions. An unthreaded hole is known as a clear hole. The thread on a bolt sometimes occupies only part of the shaft, the remainder of the shaft being clear; if the thread continues up to the head it is known as a 'set'.

See also the article on the bolt manufacturing process.

Other fastening methods

When screws and bolts cannot be used, nailing, riveting, roll pins, pinned shafts, welding, soldering, brazing, gluing, and duct tape (taping) are some alternatives.

Read more at Wikipedia.org