The HSP-I25 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 I25-850. This Hammer Spacer is used in conjunction with the OH-01 Oz-Hammer. The OH-01 Oz-Hammer is 2” in diameter. The I25-850 is 2 ½” inside diameter so we recommend using the HSP-I25 to keep the Oz-Hammer (OH-01) centered in the Oz-Post sleeve during installation.