Abstract: Sheet material is stamped between an upper die assembly and a lower die assembly. The lower die assembly includes a lower ring supported on a lower die for vertical movement. The ring cooperates with the upper die assembly in the shaping of the sheet material. Air cushion pins project through holes in the lower die and exert upward pressure on the ring. Guide pins guide the relative vertical movement of the ring. Each guide pin is secured in one of the holes in the lower die. Each guide pin has a tubular lower end portion adapted to receive one of the air cushion pins. A retainer and lockdown block is secured to each guide pin in either a ring retainer position or a ring lockdown position. The block is engageable with a retainer abutment on the ring when the block is in the ring retainer position to prevent the ring from separating from the lower die without interfering with the relative vertical movement of the ring during a stamping generation.