This very useful tool comes to us from the band instrument repair program at Minnesota State College Southeast in Red Wing, MN. It is designed to install removable rotor bearing plates. The material is PVC to allow for a soft non marring surface and the tool is designed to allow for use on all rotor sizes from horn through tuba. Simply install the rotor in the casing, install the bearing plate in the right position to the casing and use this tool against the flat face of the outside of the bearing plate while tapping on the back side of this seating tool to fully seat the removable bearing plate into the casing flush and square. Comes with a bolt to extend its use in harder to reach areas on some models of tuba with rotors. Item # P62