I posted a conversion table of American grit, Mesh and Particle size earlier in this thread. The mesh numbers are the range of particle sizes in microns since meshes at these small sizes don't exist. Mesh is a theoretical calculated number not a screen since as I said, meshes of this size don't exist. So, an 8000 grit has a mesh or range of particle sizes form 2 to 4 microns and an average particle size of 3 microns. Above 400 grit, particles are not seperated by actual meshes but by other processes which are mostly of interest to mechanical engineers involved in grinding technology.