Wrench Tools

The most common wrench tool is the open-ended hex wrench, also called a "spanner" in the United Kingdom. The opening in the end of this type of wrench has a hexagonal shape. Two parallel sides grip the bolt or nut, which slides between the gripping sides ("jaws") through a gap in one side of the hexagon. A long handle opposite this gap allows one to apply leveraged pressure. Spanners are available in either metric (millimeters) or Imperial (fractions of an inch) sizes. A good assortment of hex wrenches will include six or more wrenches of various sizes in one or the other measurement system.

An adjustable wrench has a worm screw in its head, allowing the jaws to be moved closer or further apart. This type of wrench is handier than carrying an assortment of fixed-jaw wrenches, but the jaws fit less snugly and tend to move apart a bit under pressure. Adjustable wrenches are often used on coarse pipe fittings and other large nuts or bolts, where a precise fit is not so critical. The classic monkey wrench is a type of adjustable wrench used on pipes and large nuts.

Socket wrench tools have entirely enclosed heads with more than six straight sides. The socket slips down over the top of a nut or bolt head and torque is applied. Screwdriver-like socket wrenches do not provide as much leverage as angled wrench shafts. A ratchet head allows the user to tighten or loosen a bolt with a back-and-forth wrist motion while torque is applied only in one direction.

Impact wrenches combine the sharp, great force of a hammer blow with the leverage of a socket wrench to jar loose rusted bolt threads. A cam motor shaft or bursts of compressed air rapidly apply torque to the socket to knock the stuck bolt loose.

An air wrench is often used in auto mechanic's shops, where nuts are frequently rusted and sparks in an electric motor might ignite gasoline fumes. An oil wrench is also a car mechanic's staple. It is a band of metal that wraps around an oil filter, gripping it by friction as the wrench is turned.