Wrenches, Ratchets, & Drills

The screwdriver is a device specifically designed to insert and tighten, or to loosen and remove, screws. The screwdriver comprises a head or tip which engages with a screw, a mechanism to apply torque by rotating the tip, and some way to position and support the screwdriver. more...

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A typical hand screwdriver comprises an approximately cylindrical handle of a size and shape to be held by a human hand, and an axial shaft fixed to the handle, the tip of which is shaped to fit a particular type of screw. The handle and shaft allow the screwdriver to be positioned and supported and, when rotated, to apply torque. Screwdrivers are made in a variety of shapes, and the tip can be rotated manually or by an electric or other motor.

A screw has a head with a contour such that an appropriate screwdriver tip can be engaged in it in such a way that the application of sufficient torque to the screwdriver will cause the screw to rotate.

History

Gunsmiths still refer to a screwdriver as a "turnscrew", under which name it is an important part of a set of pistols. The name was common in earlier centuries, used by cabinet makers and shipwrights and perhaps other trades.

The Cabinet-Maker's screwdriver is one of the longest-established handle forms, somewhat oval or elipsoid in cross section. This is variously attributed to improving grip or preventing the tool rolling of the bench, but there is no reason to suppose these are not rationalisations. The shape has been popular for a couple of hundred years. It is usually associated with a plain head for slotted screws, but has been used with many head forms.

Types and variations

There are many types of screw heads, of which the most common are the slotted, Phillips, PoziDriv/SupaDriv (crosspoint), Robertson, TORX, and Allen (hex).

Screwdrivers come in a large variety of sizes to match those of screws, from tiny jeweler's screwdrivers up.

If a screwdriver that is not the right size and type for the screw is used, it is likely that the screw will be damaged in the process of tightening it. This is less important for PoziDriv and SupaDriv, which are designed specifically to be more tolerant of size mismatch. When tightening a screw with force, it is important to press the head hard into the screw, again to avoid damaging the screw.

Some manual screwdrivers have a ratchet action whereby the screwdriver blade is locked to the handle for clockwise rotation, but uncoupled for counterclockwise rotation when set for tightening screws; and vice versa for loosening.

Many screwdriver designs have a handle with detachable head (the part of the screwdriver which engages with the screw), called bits as with drill bits, allowing a set of one handle and several heads to be used for a variety of screw sizes and types. This kind of design has allowed the development of electrically powered screwdrivers, which, as the name suggests, use an electric motor to rotate the bit. In such cases the terminology for power drills is used, e.g. "shank" or "collet". Some drills can also be fitted with screwdriver heads.

Read more at Wikipedia.org