The Bosch 4-1/2" X-LOCK Arbor Type 27 120 Grit Flap Disc (FDX27450120) features the X-LOCK mount, offering a wheel change that's up to five times faster than conventional interfaces. There’s an audible snap when mounting an X-LOCK wheel on an X-LOCK grinder. The wheel mounts properly without the need for a spanner wrench or flange nuts for no losable parts. The wheel is released from the grinder with the pull of a lever. Bosch flap discs are made with high-quality Zirconia grit for exceptional speed and durability in tough environments for metal grinding or blending applications. This coarse grit flap disc features a plastic backing to reduce the risk of material gouging.