Expansion tool device for socket pliers

An expansion tool device for pliers used for producing sockets at the ends of pipes made of plastic material or the like used in plumbing systems, includes a cylindrical end piece formed by the closure of several sector-shaped jaws radially mobile under the action of a conical needle operated with pliers and adapted to be axially inserted in a conical recess. It also includes an insert axially mobile between the jaws, and designed to receive the conical needle when the tool is fixed to the pliers, the insert having one end for receiving the conical needle, while its other end has a conical shape adapted to the conical recess of the jaws, the conical parts having substantially identical coning angles, but of different diameters.