The HSP-T4 is simply a square piece of steel that slides over the Oz-Hammer (OH-01) and keeps it centered on the inside of the Oz-Post sleeve when installing the T4-600, T4-850, C4-850, S4-850 and S4-600. This Hammer Spacer is used in conjunction with the OH-01 Oz-Hammer. The OH-01 Oz-Hammer is 2” in diameter. The T4-850 and other models mentioned above are a minimum of 3 ½” inside diameter so we recommend using the HSP-T4 to keep the Oz-Hammer (OH-01) centered in the Oz-Post sleeve during installation.