Features It has a ring with a rotating shaft in the center of the octagonal prism, but contains Expensive samarium cobalt (Smco) magnets, and is marked with an inert carbon mark (black) for easy identification. Compared to conventional Alnico magnets, this magnet is not only strong in magnetic force but also has little deterioration in magnetic force, so it can be used for a long time. Spec Diameter x total length: 8 x 25mm