3M�� disc pad hub has an internal threaded metal insert that threads onto the shaft of a sander and grinder to hold a disc pad face plate and fiber disc in place. Our 3M�� disc pad hub holds the face plate firmly in position to support a fiber disc with a 7/8 in center hole, which is secured to the hub with a compatible retainer nut. The disc pad hub enables operators to select face plates with 4-different densities - soft, medium, hard and extra hard - offering the convenience of using a single power tool for multiple grinding applications. Face plates are sold separately.