This socket or cap is to be used with an average sized wooden wheel caster. This piece fits into the chair or furniture leg as a receiver for the caster. The socket is pounded into the bottom so the teeth can bite into the wood. The caster stem is then pushed into the socket, allowing the top of the stem with its top knot to go past the end of the socket. The stem becomes locked into place. Since the socket is pounded into place, the caster will not fall out when the furniture is moved.
Sockets vary somewhat in size. Mostly they are 1 1/4 inches long. The base is 7/8-inch across. The top of the socket is split and narrows slightly; this allows for the stem of the caster to be locked into place. An average stem length on a caster is 1 1/2 inches. The extra 3/8-inch to 1/4 inch is shoved beyond the end of the socket