Sandpaper for random orbital sanders

Three things: the diameter of the backing pad (usually 125 or 150 mm), the fixing (almost always hook-and-loop nowadays) and the hole pattern. Multi-hole discs fit any hole pattern because there are holes everywhere – a backing pad with a multi-hole pattern does the same on the machine side.

For the workshop: P80, P120, P180, P240 in paper, P320 and P400 as mesh, plus P600 to P1000 as film for the finish. That covers everything from wood to body filler to paint.

The diameter is printed on the backing pad or in the machine’s manual. The disc must be exactly the same size as the pad: one that is too large overhangs, flaps and tears at the edge. One that is too small leaves a ring of hook-and-loop exposed – it sands along, wears out and leaves scratches.

Small DIY random orbital sanders usually have 125 mm, workshop machines usually 150 mm. The larger disc covers more area per pass, the smaller one gets into corners and along edges better.

If the holes in disc and pad do not line up, the machine barely extracts any dust. The dust stays under the disc, which clogs, gets hot and leaves pigtails. PRO CUT 150 has 15 holes and fits multi-hole pads; PRO CUT 125 has 8 holes for the standard 125 mm pattern.

Mesh discs such as PRO NET do not need a hole pattern: they are open everywhere and extract on any hook-and-loop backing pad.

Tap or blow out the backing pad, place the disc centrally with the holes lined up, and press it on firmly. If it still flies off or slips, the hook-and-loop on the pad is usually worn out – then a better disc won’t help, but a new backing pad will.