Ensure clean connections by removing paint, primer, and other contaminants from electrical grounding contact points. These discs mount to your tool with an arbor, also known as a mandrel (sold separately). The arbor’s tip pokes through the disc and fits into a drilled hole in the center of your contact point. As you sand, the tip acts as a guide to keep your tool from slipping out of the contact. Also known as non-woven or surface-conditioning discs, they're made of flexible nylon mesh to resist clogging and produce a consistent finish, even with uneven sanding pressure.