As far as I know, the light grey Scotch Brite pad is around 800 grit US/CAMI, which is the equivalent of P1600 grit FEPA, the Abralon and SiaAir scale.
I believe that when most manufacturers say "1500 grit polished", they mean 1500 grit US/CAMI, because they've been using the US/CAMI scale long before we even knew what Abralon was. If they mean FEPA (or Abralon or SiaAir), they should indicate that.
So far, when manufacturers use an Abralon pad or a SiaAir pad, they say "2000 grit Abralon" or "4000 grit SiaAir micro pad". When they they say "1500 grit polished", they don't specify the grade. So I assume they're using the CAMI scale.
1500 grit US/CAMI = approximately P3000 grit FEPA.
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