Oregon saw chain sharpening stones are popular with 12 volt chain grinders such as the Sure Sharp. These grinding stones are made of vitrified aluminum oxide. They are soft enough to quickly remove material, but hard enough to keep their shape through several sharpenings. Shafts are approximately 1/8" in diameter and are non threaded.. Note: Some 12 volt chain grinders such as the Granberg Grind-N-Joint require stones with threaded shafts. These stones will not work on those grinders. Be sure to check before ordering.. .