socket wrench

A socket wrench set. The rows of items (from top) are: sockets, an adapter and two universal joints, extenders, and wrench

A socket wrench, more commonly referred to as a ratchet, 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.

Description

The socket wrench includes a ratcheting mechanism that allows the nut to be tightened or loosened with a reciprocating motion, without requiring that the wrench be removed and refitted after each turn. Typically, a small lever behind the socket switches the wrench between tightening and loosening mode. The sockets are attached to the ratchet through a square fitting that contains a spring loaded ball detent mechanism to keep the sockets in place. These drive fittings come in four common sizes: 1/4 inch, 3/8 inch, 1/2 inch, and 3/4 inch (referred to as "drives", as in "3/8 drive"). Despite being denominated in inches, these are international standards and no metric counterparts exist. Larger drive sizes i.e. 3/4 inch, 1 inch and above are usually reserved for use on fasteners used on larger industrial equipment, e.g. in shipyards. The sockets themselves come in a full range of inch (SAE) and metric sizes. Users are advised that the two should not be substituted for each other, even if the fit seems "close" - as it may destroy the nut or bolt head. The sole exception is the 3/4" and 19mm sockets, which vary by only one twentieth of one millimeter (less than the width of a human hair). The advantage of the socket wrench system is speed - it is much faster than a conventional wrench, especially in repetitive bolt-on or bolt-off usage.

History

First socket wrench made by J.J. Richardson, 1863

Modern Wrench

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 June 18, 1863.^[1] The first illustration of the tool appears on pg. 248 of the April 16, 1864 issue of Scientific American.^[2]

Socket types

Sockets come in a variety of types:

Number of points

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. 12-point sockets are able to be used on square nuts and fasteners, and also offer double the amount of starting points, but greatly increase the chance of rounding or slipping off a nut or fastener. Simply stated: 12-point sockets are faster and more versatile, six-point sockets are more secure.

8-point sockets are still available from some manufacturers, allowing socket users to adjust square-shaped fittings rather than hexagonal ones. They were much more easily available some years ago, but square-head bolts and nuts, once common, have become a rarity in modern toolmaking.

Shallow vs deep

A set of deep sockets on a rail.

Sockets are available in various depths, 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), a very typical example being exhaust clamp bolts on an automobile.

Some high-end 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, such as chrome vanadium 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, such as chrome molybdenum steel. 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 with greater torque (for both tightening and removal of fittings) and reduces the effort exerted by the user.

Accessories

These are some of the common accessories that are used with socket wrenches:

• 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.
• Universal joints are two articulated socket joints combined at a right angle, that allow a bend in the turning axis of the wrench. They are used with extensions for turning a bolt or nut at a difficult to access location.
• Flex handles are socket wrenches in which the drive head pivots back and forth on the handle, to allow the handle to avoid obstructions when being turned in a cramped space.
• Adapters allow sockets of one drive size to be used with wrenches of another drive size. They consist of a male drive fitting of one size attached to a female drive fitting of another size. For example, a 1/4 in. to 3/8 in. adapter allows sockets with 1/4 in. drive holes to attach to 3/8 in. wrenches.

See also

• Torque wrench

References

External links

• Table of socket and nut sizes