Pair the same disc with different tools to produce consistent finishes. Use the hole to mount on an arbor or the hook and loop to attach to a backup pad. Also known as non-woven or surface-conditioning discs, these have a nylon mesh backing that resists clogging and flexes to compensate for uneven sanding pressure. They’re good for everything from heavy rust removal and deburring to blending and paint prep. You’ll need a compatible arbor-mount backup pad or hook-and-loop backup pad.