Originally Posted by
KenWeir
No, it might as well be thought of as arbitrary.
1k grit shapton isn't the same as a 1k norton
1k grit sandpaper in the us isn't the same as 1k sandpaper in uk
Edit: there's no hard and fast rule, this grit has this size particles, because every manufacturer is different.
Edit2: other considerations might be how well the particles are bonded, that will control how much slurry you generate, and how jagged or smooth the particles are. One manufacturer may use smaller particles than another, but if those particles have more sharp corners/edges it may still cut faster than the stone with larger but smoother particles. Other manufacturers might be using different materials all together, which may cut differently