A nut is a ring with a thread on the inside, which is the difference from a union nut, which has an outside thread. The outer surface may look different, but it is designed so that it can be easily gripped with a work tool. The nut has a coupling purpose and is used for axial assembly.
Sleeve nut becomes an integral part of the connection elements such as «American», coupling, many types of fittings. It is made of different materials with a special control of the size ratio, shape, strength, purpose of the nut. The shape of the product can be cylindrical or petal, the most common option - hexagon.