Collet head at a sealing machine

A collet head for a sealing machine for the accommodation of seals, particularly threaded seals for containers, said collet head comprising a bushing having an open end toward the exterior, accommodating the seal, characterized by a flexible diaphragm (6) arranged in the bushing (3) and contractible radially inward with the aid of a pressure medium, a contractible gripping member inserted into the open end of the bushing, said gripping member having a circumference engageable with the diaphragm so as to be radially contractible upon radial contraction of the diaphragm, said gripping member comprising jaws or segments (17) circumferentially displaceable to vary the grip opening thereof, and said jaws each being provided with an edge or foot (22) extending beyond the open end of the bushing, and means positioned in the open end of the bushing presenting guiding surfaces which capture and guide the gripping member.