The Bosch 4-1/2" X-LOCK Backing Pad with X-LOCK Clip - Medium Hardness (MGX0450) features the X-LOCK mount that offers a wheel change that's up to five times faster than conventional interfaces. There’s an audible snap when mounting the X-LOCK backing pad on an X-LOCK grinder. The wheel mounts properly with the included X-LOCK clip. The wheel is released from the grinder with the pull of a lever. The pads work with Bosch abrasive fiber discs made with high-quality Zirconia grit for exceptional metal removal and finishing. Bosch X-LOCK Backing Pads are not backward compatible with standard 7/8 In. arbor mounts.