An internal wrenching nut, also known as an Allenut[1] or Allen nut, is a cylindrical nut that is internally threaded on one side and has an Allen socket on the other side; the outside of the nut is smooth or has knurling on it. The Allen socket may be 6 point or 12 point (also known as a double hex socket). They are used where hex or square nuts won't fit.[2]