Packaging includes: 4 x 877-323 Piston Driver and 6 x 878-303 Bumper Replacement models: 877-323, 883-511, 878-303, 878-649, 877-376, 878649 The piston drivers are made of Heat treated tool steel 6150, the rock well hardness is 50-52, and they are aerospace grade # 2024 Aluminum piston For Hitachi NR83A, NR83AA, NV65AA, NV75A, NV83A, NV65AC, NR83AA3, NV85AG, NR83A2 (S), 83AA2, NR83AAC, NR83A3S, NR83A3, NR83AAM4, NV83A3, NV83A2, NV83A4, and NV83A2