Abstract: Rapidly releasable attachment of an abrasive disk to a rotary grinder is provided by fitting the disk with a disk retention adapter which clamps onto the disk and is provided with retention means extending from the non-abrasive bearing surface, a also providing a lock-nut assembly for mounting on the drive shaft of the rotary grinder which comprises a number of detents and detent access slots which permit the retention means to be inserted into the slots and, by a simple axial rotation move the retention means into the detents to lock the disk into position.