PURPOSE: To form grooves in the trunnions of a blank by sliding the blank between two surfaces to a punch which occupies a space in the circumferential direction between the two trunnions of the blank between the two surfaces to form parallel guide surfaces and is provided with a forming edge.

CONSTITUTION: An element having trunnions 2 which is arranged in the radial direction and provided with lubrication grooves 3 is manufactured around the central axis U. A blank of the trunnions is arranged between a punch 18 and a floating punch 19 which occupy a space in the circumferential direction between the two trunnions of the blank between the two surfaces of parallel guide surfaces 12 and are provided with a forming edge 9 on each of the two trunnions. The blank is voluntarily arranged between the forming edges of the punch by sliding the blank between the two surfaces to give relative motion to the punch for the blank. Thus, the lubrication grooves can be formed in the trunnions, the heat treatment for hardening the blank is applied and the bearing surface of each trunnion is ground to manufacture a product.