These aluminum single speed cogs feature extra tall teeth for reliable chain retention when using chain tensioners. They are reversible and feature a 4.5 mm width at the base that won't dig into your freehub body. Compatibility - These will fit on Shimano Hyperglide style freehub spline (geared or single speed). - Not compatible with Shimano Microspline or SRAM XD freehubs. - Designed to work with any chain through 12-speed - - - Tooth width optimized for 9, 10, and 11-speed chains - - - Not compatible with Campagnolo Ekar 13-speed chains