Matched set issue; bronze-aluminum81-4-4-11; 3.869/3.871 diameter each; first piston 1 external 0.275/0.280 x 3.501/3.506 diameter ring groove and 1 internal 0.275/0.280 x 1.125 ring groove; second piston 1 external 0.275/0.280 x 3.501/3.506 ring groove and 2 interna grooves; first groove 1.750/1.766 x 0.125 w