Wrench

Spanner'' redirects here. For spanner screwdrivers, see spanner (screwdriver).''

A wrench, also known as a spanner, is a hand tool generally used for turning fasteners, particularly nuts and bolts. Commonly, it consists of a single handle and a pair of jaws with parallel, typically smooth faces, though some designs feature only a single jaw.

Wrenches may be open or closed; open wrenches may be fixed or adjustable. A closed wrench is known as a box wrench. A combination wrench features a box wrench at one end of the handle, and an open wrench of the same size at the other end.

Comparison with pliers
A properly-sized wrench fits snugly around the nut (or other work piece), turning it without damaging it. A loosely-fitting wrench may round-off the fastener's corners, making the fastener more difficult to remove. An overly large wrench, unless adjustable, will not be able to turn the fastener at all.

In comparison, a pliers' jaws are inherently adjustable, enabling it to grasp a wide range of fastener sizes. The textured jaws, however, make the pliers likely to mar the fastener. Pliers are thus more of an all-purpose tool, with wrenches more precision and kinder to the fastener.

Open-ended
Open-ended wrenches form a C shape, wrapping around three sides of the fastener. These may be adjustable or of fixed size. By their nature, open-ended wrenches don't grab a fastener's head as firmly as a closed (box) wrench, leaving the open-ended wrench more prone to slipping off, damaging the fastener and the users knuckles.

Adjustable
Adjustable wrenches, such as the open-ended adjustable wrench, or C-wrench, have the benefit of fitting a variety of fasteners, at the drawback of a looser, more-likely-to-slip fit.

Traditional designs
Box wrenches are traditionally made with a six-point (six-sided) or twelve-point (twelve-sided) opening. Six-point wrenches are stronger, as they have more metal between the points. They can only grip a fastener in six different orientations, however, and cannot turn square fasteners. Twelve-point wrenches are more prone to failure (or to rounding-off the corners of the fastener), but are more versatile, since they can be applied in any of twelve different orientations. Twelve-point wrenches can also turn square fasteners.

Side-gripping
To combat rounding-off, one newer design has hollowed-out points. This enables the wrench to grip the sides of the fastener, rather than its corners, preventing round-off.

Spline
Spline openings are able to turn a greater variety of fasteners, including four-point, six-point, twelve-point, and external Torx.