5/8" - 11 NC threaded arbor. .014" wire size, 8,500 Max RPM. Heavy duty cup brushes with arbor adapters and threads to fit most grinders. Made with high quality tempered wire. Provide fast cutting action for removal of light encrustation of scale, rust, paint or weld splatter The relative high flexibility of Firepower wire cup brushes allows cleaning on irregular surfaces as well as flat surfaces. These brushes are designed for use on portable power tools.