Sockets are basic tools typically used to remove or tighten nuts and bolts, and come in a wide variety of types aimed at making jobs easier, fitting special nut/bolt heads, or both.
Deep Wall Sockets
Deep wall sockets allow for room above the head of a nut so that a bolt's thread or something above the nut/bolt to be avoided when installing or removing them. Deep wall sockets can also be used as a short extension beyond the length of a standard socket.
Impact Grade Sockets
When using an impact tool, impact sockets must be used. Impact sockets are typically thicker than normal sockets and have a matte black coating to make them easy to identify.
Swivel-head sockets allow for the ratchet, typically with an extension attached, to be used at a different angle than the head of the nut or bolt, allowing access to tight spaces or the use of an extension that normally wouldn't be able to be used. Swivel sockets are also available in impact grade but typically have a different design to handle impact torque.
6-Point Versus 12-Point
Sockets will often come as a 6-point or a 12-point, and they both have advantages and disadvantages. A 6 point socket tends to be stronger because there is more material in the wall of the socket. The 12-point socket is easier to get onto the head of a nut or bolt, and is able to be used on 12-point nuts and bolts.
Thin Wall Sockets
Sometimes a typical socket is too thick for the components around the head of a bolt or nut, so a thin wall socket becomes useful. The disadvantage with a thin wall socket is that it isn't as stong, so it can't handle as much torque as a normal socket.
Sometimes sockets have a special design to fit specialty nut or bolt heads, or to be used in a different way.
Torx Head Sockets
Torx head sockets have a torx bit permanently installed into a socket. Torx head sockets are typically labeled with a T in front of them, such as with T15, and a smaller number means a smaller head size.
Allen Head Sockets
Allen head sockets have an allen head bit permanently installed into a socket. Allen head sockets come in both Metric and SAE sizes.
E-Torx Head Sockets
E-Torx sockets are shaped like the reverse of Torx, as if they could accept a Torx head bit into them. E-Torx sockets are typically numbered with an E in front of them, such as with E18, and a smaller number means a smaller head size.
Spline Drive Sockets
Spline drive sockets have 12 splines in them that are able to grab many types of outward-facing nut/bolt heads, including 12-point, 6-point, E-Torx, slightly rounded heads, spline heads, and square heads. Spline drive tools are typically labeled with the type of 6/12 point head it will fit.
Triple Square Sockets
Triple square sockets look like a 12-point allen socket, but the angles are different and require that socket in particular when a bolt is designed with a triple-square head.
Crankshaft Nut/Bolt Sockets
Crankshaft nuts and bolts are notoriously tough to remove, and some sockets are specifically designed to counter this by being extra heavy impact grade. They are much thicker not just for added weight, but to apply extra momentum to each impact hit, helping break the nut/bolt loose.
Oil Filter Sockets
Oil filters typically have a shaped head to them that allow an oil filter socket to be used. These sockets have one or two sizes in them and cop the top of the oil filter. The socket is typically a 3/8ths drive, and allows for the use of extensions and other components a typical socket can be augmented with.
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