Socket wrench
A socket wrench is a type of spanner that uses a closed socket format, rather than a typical open wrench/spanner to turn a fastener, typically in the form of a nut or bolt.
The most prevalent form is the ratcheting socket wrench, often informally called a ratchet. A ratchet incorporates a reversible ratcheting mechanism which allows the user to pivot the tool back and forth to turn its socket instead of removing and repositioning a wrench to do so.
Other common methods of driving sockets include pneumatic impact wrenches, hydraulic torque wrenches, torque multipliers and breaker bars. Some lesser known hybrid drivers include striking wrench tools with square drive, and hydraulic impact wrenches.
Interchangeable sockets
The basic contemporary form of socket is hexagonal, referred to as "6-point" for the pointed intersections where its six solid sided facets meet.Male drivers are also produced for use with socket head cap screws, and are often called Allen drivers or the generic term male bit drivers.
The principal advantage of interchangeable sockets is that, instead of a separate wrench for each of the many different fastener sizes and types, only separate sockets are needed for each size and type. Because of their versatility, nearly all screw and bolt types now have sockets of different types made to fit their bolts or nuts. Sockets often come as a "socket set" with many different sizes or types of sockets to fit the heads of different-sized fasteners. A ratchet of the "set size" is often included with the socket set. Sockets are commonly available in fractional inch and metric sizes, and in short and longer varieties.
Square drive
The interchangeable sockets are attached to the driving tool via a male/female square connection fitting. Standard sizes of square drives around the world include square drive sizes. -inch square drive is less popular, as are No. 4 and No. 5 spline drives specified in ANSI B107., and sizes are the most commonly found variants. This wide range of square drive sizes provides for a wide variety of socket types and sizes to suit small to very large nuts and bolts. Some square drivers have a through hole to attach the socket to the driver, a locking pin, or friction ball. Some common hand ratchets employ a quick release button on their top for quick socket release of smaller sockets. The tool chosen to drive the socket wrench ultimately supplies the mechanical advantage needed by the user to provide the torque needed to loosen or tighten the fastener as may be required. Larger drivers are typically used with higher torque, while smaller drivers are used for convenience in smaller low torque applications. Given the limits of human strength and fatigue, torque above of torque will generally involve some kind of power assist, instead of the user simply pushing on the handle of a wrench. Very large sockets and drivers are typically powered by hydraulics to achieve torque.History
Wrenches in the form of sockets—that is, a female driver to envelop the male head of a fastener—have existed for centuries. Early examples include the keys used to wind clocks since the Middle Ages. The heads and sockets were typically square; hex heads eventually became more common starting in the 20th century. The ratcheting socket wrench, with interchangeable sockets, was invented by an American, J.J. Richardson, of Woodstock, Vermont. The tool was patented through the Scientific American Patent Agency on June 16, 1863. The first illustration of the tool appears on p. 248 of the April 16, 1864 issue of Scientific American. In current American English usage, the term "socket wrench" describes the wrench, not the socket. However, the term "socket wrench" is not used in British English.Square heads and sockets were the easiest to make in the era when hand filing was the typical method of manufacture. With the proliferation of modern manufacturing methods it became just as easy to make hex heads and sockets as square ones. The hex form allows easier wrenching in confined surroundings, because fewer degrees of arc are needed on each swing before it is possible to reposition the wrench onto the next set of flats. Ratchet wrenches further reduce this problem, as the wrench need only swing as many degrees as it takes for the ratchet pawl to catch the next tooth.
The quick release feature common to ratchets was invented and patented in 1964 by Peter M. Roberts.
Related tools
Fixed socket
Interchangeable socket
Ratcheting
| Image | Name | Description |
| 150px | ratcheting socket wrench | The most common type of socket wrench. The ratcheting mechanism 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 on the ratchet head switches the wrench between tightening and loosening mode. These drive fittings come in four common sizes: inch, inch, inch, and inch. Despite being denominated in inches, these are trade names, and manufacturers construct them to 6.3 mm, 9.5 mm, 12.5 mm and 19 mm, having been rounded to a reasonable, if haphazard, metric value. Larger drive sizes such as 1 inch and above are usually only encountered on fasteners of larger industrial equipment, such as tractor-trailers, large cargo aircraft and passenger airliners, and marine work. The sockets themselves come in a full range of inch and metric sizes. The advantages of the system of a ratchet wrench with indexable sockets are speed of wrenching and efficiency of tooling cost and portability. Fine-tooth ratchets have finer teeth on the ratcheting components; these can be useful for tighter locations. Dual-pawl ratchets click twice for each tooth on the gear, effectively doubling the granularity of the mechanism. |
| 150px | click-style torque wrench | Normally ratcheting and click when a preset torque is reached. Some torque wrenches have digital read-outs of torque. Other types of torque wrenches exist such as torque limiting that only allows a preset torque to be reached before they slip. For some applications, torque multiplying devices are used with a torque wrench. |
| 150px | flex-head ratchet | Ratchets in which the drive head pivots or swivels back and forth on the handle at a pivot to the rear of the ratchet head. |
| 150px | swivel-head ratchet roto-ratchet | Ratchets in which the entire ratchet head swivels with handle attachments on the side of the ratcheting head rather than the rear of the ratcheting head. |
| palm ratchet | Ratchets with a knurled palm sized circular ratchet handle with reversible socket attachment useful for rapidly loosening or tightening a bolt or nut. They come in a variety of sizes. | |
| rotator ratchet | Allow the socket to be twisted by twisting the ratchet handle around the handle axis. Requires less than one degree arc swing to rotate socket, which makes them ideal for very tight spaces. | |
| gearless ratchet | A ratchet that doesn't use gears, but instead uses bearings to provide virtually no arc swing nor produces an audible or discernible click. This is not commonly used as the regular geared ratchet. |
A number of other specialized ratchets—with hammer heads, multiple drive sizes, and other unusual features—are built by various manufacturers.
Non-ratcheting
| Image | Name | Description |
| 150px | breaker bar power bar flexible handle | A bar that attaches to a standard socket. Breaker bars are usually longer and built more sturdily than a standard ratchet handle and have a swiveling head that attaches to the socket. Breaker bars are used to break loose tight fasteners because their additional length and strength allows the same amount of force to generate significantly more torque than a standard length socket wrench. The use of a breaker bar also avoids potential damage to the ratcheting mechanism of a socket wrench. Once the fastener is "broken loose," it can be turned with a socket wrench or by hand. |
| 150px | beam-style torque wrench | Usually non-ratcheting, made to attach to standard sockets. By monitoring the degree of beam deflection, the applied torque can be determined. |
| 150px | speed handle speed brace | A crank-shaped handle that rapidly loosens or tightens a fastener when used with the correct socket. It works much like a brace and bit adapted to sockets. |
| 150px | spinner handle socket handle | A screwdriver handle with a male drive end for attaching sockets. |
| offset drive | A fixed drive where the head spins relative to the handle spinning, with the handle having a drive attachment where a ratchet or other socket wrench can be attached. |