Sanding disc size, fixing and hole pattern
Diameter alone does not determine a suitable sanding disc.
Match the backing pad
Check the disc diameter and attachment system against your sander’s instructions. Hook-and-loop and adhesive discs are different fixing systems.
Check dust extraction
For punched discs, line up the disc holes with the pad’s extraction pattern. A matching diameter does not prove that the holes align. Check mesh abrasives and interface pads with the tool and accessory maker.
Choose the abrasive for the job
Grit and abrasive material depend on the surface and finish. Start with manufacturer guidance for your material. Use appropriate dust extraction and follow the tool’s protective-equipment instructions.