A spark plug socket is a specialized, deep-length socket designed to fit over the plug terminal and insulator while it grips the hex nut for removal. Most spark plug sockets come in two sizes: 5/8 inches and 13/16 inches, accommodating standard spark plug brands such as Bosch, Champion and NGK.
The spark plug socket, which contains a rubber lining that prevents slippage, is either a removable piece that attaches to a ratcheting socket wrench or permanently joined to the end of a T-handle. A universal spark plug socket contains a movable joint that allows for rotation in hard-to-reach locations. Some spark plug wrenches mount a handle on the side of the socket. Other socket wrenches are tubular pieces with holes in the side where a T-bar is inserted to turn the socket.