Same 100 mm grinder, different grit: how choosing the wrong flap disc grain wastes the whole pass
Flap discs for a 100 mm angle grinder come in different grits, and the grit decides what the disc does: coarse grains cut fast and leave deep scratches, fine grains remove little material but leave a surface you can finish from. If you buy one disc and expect it to do both, you spend twice the time: a coarse disc will never give you a painted-ready surface, and a fine disc will burn through discs trying to take off a weld bead. The thickened backing on this one is aimed at longer life under pressure, which matters on steel plate rather than light touch-up work. Two things to settle before ordering: which grit or grit set the listing actually ships, and the maximum RPM printed on the disc, which must be at least your grinder's no-load speed. Always wear goggles and a dust mask.