Also known as bolster, A piece of steel that is tightly fixed in a die. The insert may be used to fill a cavity, to replace a portion of the die with a grade of steel that is better suited for service at that point, or to function as a small die with the impression fastened to a master die.... More holder, can. Used to locate, clamp and support The metal blocks into which forging impressions are machined and from which forgings are produced., The machined recess in a die that gives the forging its shape. assemblies or The machined recess in a die that gives the forging its shape. inserts.