A self-actuating tooling die located beneath an industrial press impact zone clamps a the tongue of an end ring side-to-side to hold it dimensionally stable during a pressing operation that clinches a nut to a hole in the tongue. The tooling die comprises a cone-shaped split collet fitted into a corresponding cone-shaped receptacle in the die housing. As the installation force of the press forces the collet into the receptacle, jaws of the collet grip the tongue a corresponding amount. At a pre-determined point of advancement, the collet bottoms out against a stop in the socket to hold the tongue in its pre-installation relaxed shape and size. A spring-loaded stepped pin, which reciprocates within an axial bore of the die, centers the nut and hole in the tongue during installation and later ejects the completed assembly.