Abstract: This relates to special tooling for forming metal end units for use in conjunction with cans for carbonated beverages and the like wherein the formed end unit is provided with an integral reinforcement in the form of a countersink so as to increase the buckle strength of such an end unit when it is formed of thin metal. Previously there has been developed tooling for forming such an end unit which, while it is commercially satisfactory, did not produce end units having the required buckle resistance. That tooling has been modified by changing the configuration of a punch core so as to eliminate a previously formed cylindrical extension of the end unit chuck wall and a countersink starter. The punch core cooperates with a die core to clamp a center panel of a formed end unit shell so as to move the center panel reversely of its forming direction and to effect a folding of an outer peripheral portion of the center panel in a lower part of the previously formed chuck wall into the required countersink.