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.

18 US Mesh defined as 1000 µm screen aperture
Sieve Size No.	(US Mesh) Theoretical Sieve Opening	(µm)Sieve Opening ASTME II	(µm) FEPA Size No.
18	1000	1000	D1001
20	841	850	D851
25	707	710	D711
30	595	600	D601
35	500	500	D501
40	420	425	D426
45	354	355	D356
50	297	300	D301
60	250	250	D251
70	210	212	D213
80	177	180	D181
100	149	150	D151
120	125	125	D126
140	105	106	D107
170	88	90	D91
200	74	75	D76
230	63	63	D64
270	53	53	D54
325	44	45	D46
400	37	38	D39
500		32	D33
600		25