Socket wrench

"Socket set" redirects here. For the software program, see SOCET SET.

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

A socket wrench is a wrench with interchangeable heads called sockets that attach to a fitting on the wrench, allowing it to turn different sized bolts and other fasteners. The most common form is a hand tool popularly called a ratchet consisting of a handle with a ratcheting mechanism built in, so it can be turned using a back-and-forth motion in cramped spaces. A socket has a cup-shaped fitting with a recess that grips the head of a bolt. The socket snaps onto a male fitting on the handle. The handle supplies the mechanical advantage to provide the torque to turn the socket. The wrench usually comes in a socket set with many sockets to fit the heads of different-sized bolts and other fasteners. The advantage of a socket wrench is that, instead of a separate wrench for each of the many different bolt heads used in modern machinery, only a separate socket is needed, saving space.

The other common form factor is a power tool version in which a socket set is used with an impact wrench. The wrench is usually powered pneumatically, although electric versions are not uncommon. Hydraulic motor versions are rare outside of heavy industry. The sockets for impact duty (called impact sockets) are made with higher bulk and strength than those for hand-tool duty. They are typically finished in black oxide rather than the chrome plating typical of the hand-tool variety.

The principal application of socket wrenches is to loosen and tighten fasteners such as nuts and bolts.

Nut drivers also use a female socket to envelop and drive a male fastener head. From an etic perspective they are a variation of the socket-as-wrench theme, but they are not emically classified in English by the name "socket wrench".

Description

The socket wrench typically is of the ratchet type. 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. 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 such as 1 inch and above are usually reserved for use 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 nonratcheting wrenches, with every size head having its own handle).

History

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

Modern ratchet wrench.

Wrenches in the form of female sockets 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, USA. The tool was patented through the Scientific American Patent Agency on June 18, 1863. The first illustration of the tool appears on pg. 248 of the April 16, 1864 issue of Scientific American.

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, such as milling, shaping, broaching, and advanced die forging, 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. Of course, 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.

Socket Wrench Types

Socket wrenches come in a variety of shapes, lengths, and styles depending on their intended purpose:

Number of Points (shape)

Sockets are colloquially referred to by counting the number of "points" (pointed corners of walls) present in the shape of the nut opening. For example, the hexagon shape is commonly called a "6 point" socket because the hexagon forms 6 "points" where walls intersect to create sharp pointed corners. The vast majority of common nut and bolt heads are produced with the 6-point hexagonal gripping shape. Square 4-point, octagonal 8-point, and 12-point bolts are used less frequently, typically for special applications or particular industries such as aircraft. With rail cars, valve adjustment screws and pipe plugs the 4-point square shaped driver can still be found in wide use. Nuts and bolt heads are also produced in 12-point shapes and various types of splines more common to aircraft and aerospace applications. Most manufacturers of sockets produce them in 6-point (hexagonal) and limited sizes of 12-point (double-hexagonal) configurations. A few manufacturers produce less common shapes of sockets such as 8-point (double-square), 8-point (octagon) and 4-point square among other unusual shapes like spline and clutch drive to name a few.

When working with common 6-point hexagonal fasteners the 12-point shaped socket wrench offers double the amount of starting points or possible positions by which to put the socket on the nut, and this versatility is the main purpose of the 12-point shape found in socket wrenches (in addition to matching up perfectly with 12-point bolt heads found primarily in aerospace/military applications). The same principle of doubling the available positions for working with the socket is also true with regards to 8-point double-square sockets as they are used on square 4-point nuts.

Due to the twisting or cam action of the socket, most of the torque is applied at or near the corners of the nut or bolt. Under load, the flats of the nut are not touching the socket at all, it is only the surface to surface contact happening in the corners which bears any load. When the corners of a bolt head or nut begin to become worn or damaged, the material the nut is made from can eventually smear or tear under load and create a situation where the corners are effectively "rounded off" and no longer form a crisp shape anymore. When this happens, the nut or bolt can no longer be turned without special repair or extraction tools sometimes costing thousands of dollars (USD). Because of how costly this "rounding" can be when it involves large equipment which cannot be assembled or disassembled due to a rounded off fastener head, many efforts have been made to avert this problem. Over the years several different manufacturers have employed use of convex walls and other design improvements to the socket geometry in order to direct the torque farther away from the corners, and towards the thicker sections of the nut or bolt head where it is stronger; thus reducing the likelihood of rounding off corners of fasteners under high loads. These designs have been met with good commercial success and popularity, especially in the automotive maintenance and repair sector.

A common misconception is that a 12-point socket is more likely to round off the corners of a nut or bolt than a 6-point socket. In fact, since the torque is applied at the corners of the fastener, the two sockets have the same number of contact points, apply the same amount of torque, and one is no more likely to round off the corners than another. Although extensive industry testing documents this fact, the myth persists.

Standard Length vs Deep Length

A set of deep sockets on a rail.

Sockets are available in various depths, often divided by most manufacturers into two categories of "standard" and "deep" according to the ANSI or DIN standard they are made to and the tolerances allowed by those specifications for each length of socket. Because the standards allow for some flexibility in tolerances, it is common to see two manufacturers make Deep sockets of the same size but with slightly different depths even though both meet the same specification. Standard length, 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.

Although most manufacturers offer only those sizes and depths described within the common ANSI or DIN specifications, some exceptions do exist. Specialty manufacturers such as IMPERIAL-Newton Corp offer an expanded range of "extra deep" sockets for special industrial applications; and popular brands like Snap-on or Mac Tools offer what are called "semi-deep" or "mid-length" sockets, which provide much of a deep socket's depth, while fitting in tighter locations.

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. Regular chrome plated "hand sockets" like those commonly included with ratchet wrench tool sets are definitely not suitable for this kind of high load impact application. Hand sockets are made of a somewhat strong, but relatively soft steel which is economical and suitable for low torque applications. If used with an impact wrench, hand sockets can shatter explosively if they break. Impact sockets are specifically designed and manufactured for impact use, and made from a tougher and more ductile alloy steel which is then heat treated for extra durability. These impact sockets are rarely if ever chrome-plated, as chrome will chip off under impact, and the process of chrome plating causes hydrogen embrittlement if applied to hardened steel impact sockets. Instead, impact sockets are most commonly finished with a surface conversion of black oxide or other coating to provide corrosion protection and improved appearance over bare steel. Although ordinary sockets should never be used with impact wrenches, impact sockets can be used with hand socket wrenches and other hand drivers. In some breaker bar use, and especially in cheater bar use (which is usually ill-advised anyway), a user may feel safer using an impact socket.

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 sockets 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

External links

• Table of socket and nut sizes