A socket wrench (or socket spanner) is a type of spanner (or wrenchSocket wrench: A wrench usually in the form of a bar and removable socket made to fit a bolt or nut Merriam-Webster in North American English) 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.“Socket wrench: A ratchet tool with a series of detachable sockets for tightening and loosening nuts of different sizes.“ Oxford Dictionaries
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 (typically powered by on site hydraulic power such as present with military tanks, and many rail car applications).
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 (trademark) 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 (shallow) and longer (deep) varieties.
Square drive The interchangeable sockets are attached to the driving tool via a male/female square connection fitting (called the square drive). Standard sizes of square drives around the world include square drive sizes (dimensions up to 1 inches are standardized in ANSI B5.38-1958, a de facto international standard with no metric equivalents). -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 (using a retaining ring with O-ring and pin type, or single piece molded retaining rings), 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 (indexable) 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 (where nearby obstacles obstruct the swing of the wrench), 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 Image Name Description lug wrenchwheel brace A non-ratcheting socket wrench where the socket is attached permanently to the end of a L-shaped, or X-shaped bar. They are designed as special use socket wrenches for loosening and tightening lug nuts on automobile or truck wheels. nut driver A screwdriver-type handle for hand turning with a built-in female socket at the end of either metric or fractional inch sizes. May be of different lengths. flex-head socket wrenchSaltus wrench Combination wrenches with a fixed socket in place of the box end. T-handle A socket attached to a T-handle that is used for leverage. The socket may be fixed or sliding. tuning wrench Used to tune some musical instruments' strings. spark plug wrench tube spanner
box spanner A tube with six-sided sockets on both ends. It is turned with a short length of rod (Tommy bar or T-bar) inserted through two holes in the middle of the tube. Often used in situations where a common-sized fastener is recessed deep in a blind hole with minimal radial clearances for using a standard wrench/ratchet handle, such as automotive spark plugs or plumbing/tap hardware.
Interchangeable socket
Ratcheting
Image Name Description 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 (referred to as "drives", as in " drive"). Despite being denominated in inches, these are trade names (common product name), 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 (articulated lorries), large cargo aircraft and passenger airliners, and marine work (merchant fleets, navies, shipyards). The sockets themselves come in a full range of inch and metric sizes. ("SAE" is often used as a blanket term for the nonmetric sizes, despite the technical inaccuracy of that usage.)
The advantages of the system of a ratchet wrench with indexable sockets are speed of wrenching (it is much faster than a conventional wrench, especially in repetitive bolt-on or bolt-off usage) and efficiency of tooling cost and portability (it is much more efficient than a set of non-ratcheting wrenches, with every size head having its own handle).
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. 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. 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. swivel-head ratchetroto-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 ratchetA 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 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. 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. 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. spinner handlesocket handle A screwdriver handle with a male drive end for attaching sockets.offset driveA 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.
Powered There are also power tool versions of "air" (pneumatic) ratchets which use compressed air power to drive air powered socket wrenches which tighten or loosen nuts or bolts. A second major variety of compressed air powered tools are impact wrenches which are used for common tasks such as lug nuts on wheels. Electric powered impact wrenches for the same tasks are not uncommon. Small cordless 12 volt and 18 volt impact drivers are often used today as powered ratchets to remove and install nuts and bolts. Hydraulic motor ratchets with their characteristic higher torque are rare outside heavy industry. The sockets used for impact duty (called "impact sockets") are made with thicker walls and tempered to a lower hardness so as not to shatter under the impacts of the impact tool. They are typically finished in black oxide rather than the usual chrome plating of the hand-tool variety. Standard sockets (i.e. non-impact sockets) may shatter if used with impact wrenches, presenting a safety risk.
Socket types