HSP-T46 Hammer Spacers are a square tool that slides over the Oz-Hammer (OH-01) and keeps it centered on the inside of the Oz-Post sleeve when installing the T46-850. This Hammer Spacer is used in conjunction with the OH-01 Oz-Hammer. The OH-01 Oz-Hammer is 2" in diameter. The T46-850 is 3-1/2" x 5-1/2" inside diameter so we recommend using the HSP-T46 to keep the Oz-Hammer (OH-01) centered in the Oz-Post sleeve during installation. Only one spacer and one driver is needed to drive all corresponding posts.