4.5", 60 grit, x-lock arbor, type 27, flap disc,fixed mount & high quality zirconia grit, features snap on mounting & wheel release lever, the wheel mounts properly without the need for a spanner wrench or flange nuts, backward compatible with standard 7/8" arbor mounts, durable material specially formulated zirconia grit provides for more durability & faster stock removal, application focused designed specifically for fast material removal & use with small angle grinder, precision manufacturing optimized flap design for less vibration & improved grinding speed.