A type of wrench is a tool used to tighten or loosen nuts and bolts. SPANNER, SOCKET, ALLEN, Stillson, MONKEY, and RATCHET are all types of wrenches. A SPANNER is a wrench with two ends that fit into the head of a bolt or nut. A SOCKET is a wrench with a hollow end that fits over a nut or bolt head. An ALLEN wrench is a type of wrench with a hexagonal shape that fits into the head of a bolt or nut. A Stillson wrench is a type of adjustable wrench with a curved jaw. A MONKEY wrench is an adjustable wrench with two parallel jaws. Finally, a RATCHET wrench is a type of wrench with a ratcheting mechanism that allows it to be used in tight spaces.