How is diamond size measured?

Diamond abrasives are traditionally sold in US mesh size ranges, these mesh sizes are defined by the mesh size of sieves used to separate the diamond particles. The sieve sizes are graduated and defined by the number of lines per inch of each sieve e.g. 50 lines per inch or 20 lines per inch. The diamond is then sold in overlapping mesh size ranges. The industry size specifications are laid down and governed by two bodies, these are ANSI and FEPA. The specifications are completely interchangeable. ANSI specify a US mesh size while FEPA sizes are quoted as a DIN size. Element Six saw diamond products are available in the following US mesh/FEPA DIN sizes. 20/30, 25/35, 30/40, 35/45, 40/50, 45/60 & 50/70. This means for example in a sample of 40/50 US mesh diamond most of the material would fall between the 40 mesh and the 50 mesh sieve. International standards permit that a small amount of oversize and undersize material is permitted, but this is usually no more than 2-4%. Element Six products are processed to standards much tighter than ANSI/FEPA specifications.