1. A great combo of valve seat grinder stone holder 9/16" inches with 5 pcs Black & Decker Valve Seat Grinding Stem Pilots. 2. This set includes Valve Seat Grinding Stem Pilots of 4.5mm + 5mm + 5.5mm + 6mm + 7mm having top of the pilots are of 0.375" inches. 3. This set also includes Heavy duty Black & Decker style valve seat grinder stone holder thread 9/16" inches with hex ball. 4. These pilots Compatible with the holders of Black & Decker. 5. These Black & Decker pilots and Black & Decker holder made of selected steel.