A socket wrench is a type of wrench, or tightening tool, that uses separate, removable sockets to fit many different sizes of fittings and fasteners, most commonly nuts and bolts. It generally includes a ratcheting mechanism that allows the nut to be tightened or loosened with a continuous motion, rather than requiring that the wrench be removed and refitted after each turn. Typically, a lever behind the socket switches the wrench between tightening and loosening modes. The sockets attach to the ratchet through a square fitting that locks onto them and come in four common sizes: 1/4 inch, 3/8 inch, 1/2 inch, and 3/4 inch. These different square measures are described as "drives." (Despite being denominated in inches, these are international standards and no "metric" counterparts exist.) Larger drive sizes such as 3/4 inch, 1 inch, and above are usually reserved for use on fasteners used on larger industrial vehicles.
The modern socket wrench, with interchangeable sockets, was invented by an American J.J. Richardson, of Woodstock, Vt. The tool was patented through the Scientific American Patent Agency on the 18th of June, 1863. The first illustration of the tool appears on pg. 248 of the April 16, 1864 issue of Scientific American. Previously, sockets were attached to the handle, so different-sized nuts required different wrenches.
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Socket types
Sockets come in a variety of types:
6-point vs 12-point
Modern nuts and bolt heads are made with hexagonal gripping surfaces and as such limit the number of positions a wrench can adopt when placed over them. Sockets are produced in 6-point (hexagonal) and 12-point (double-hexagonal) configurations. When working in a confined area with limited turning space, 12-point sockets double the number of starting positions. 6-point sockets, however, offer a better grip on fittings and are less likely to slip and round off the corners with continued use and are generally preferred for damaged nuts and bolts. 8-point sockets are available from some manufacturers, allowing socket users to adjust square-shaped fittings rather than hexagonal fittings.
Shallow vs deep
Sockets are available in various lengths, often divided by manufacturers into two categories of "standard" and "deep." Standard, otherwise known as "shallow" sockets, have a lower profile and allow a user to access nuts in narrow spaces. Deep sockets are useful for turning nuts onto bolts when the bolt extends upwards into the socket (as in the case of many bolted joints). Some manufacturers, such as Snap-on or Mac Tools, offer what are called "semi-deep" sockets, designed for cases where marginal depth is desirable.
Impact sockets
High strength fasteners in demanding situations often require the use of an impact wrench or impact driver to deliver the amount of torque required to tighten or loosen them. Standard sockets are made of a strong, but brittle steel. When used with an impact wrench they can shatter explosively if they break. Impact sockets are made of a weaker, but more malleable steel that will deform and split instead of shattering. These sockets are not chrome-plated, as chrome can chip when used with impact wrenches. Instead, they are made with a coating of black oxide or a plastic coating to prevent corrosion. Impact sockets can be used with hand-held drive tools; however, users often attach them to pneumatic tools, such as the aforementioned impact wrench, and use compressed air to place and remove fittings. This allows adjustments at greater torques (for both tightening and removal of fittings). Furthermore, it often reduces the effort exerted by the user.
Accessories
Extensions, sometimes called "extender arms," allow access to nuts that are difficult to reach, typically in automotive applications. A breaker bar is an extended-length handle for socket wrenches that adds extra torque for loosening strongly tightened or frozen fasteners. Flex handles are socket wrenches that lack a ratcheting action, but the drive tip instead pivots back and forth in one direction, offering more torque.
