The Rebuild Kit is for our PGD2000 & PGD2000X Drivers and includes Viton O-rings for the hammer and anvil, O-rings for the damper assembly, housing O-ring seal, and EP 0 grease. A post driver works by simply moving compressed air. We recommend you replace all O rings annually or if you notice inadequate performance. Replacing these O rings will restore the compression and performance of your driver.