If you take a (1) inch space and add wires to it, the number of openings within the 1″ space is defined as mesh. For example, if the 1″ space has ten openings for particles to fall through, then that sieve would be called a 10 mesh sieve. Typical sieve sizes are 4, 5, 6, 7, 8, 10, 12, 14, 16, 18, 20, 25, 30, 35, 40, 45, 50, 60, 70, 80, 100, 120, 140, 170, 200, 230, 270, and 325.
A grit is defined as a particle size similar to mesh, but a grit is actually a distribution of various particle sizes that meet a standard. For example, 36 grit is defined by 5 sieves; 20, 30, 35, 40, and 45 mesh. These sieves are nested together on a machine and shaken. The sieves are removed one at a time and the amount of material resting on each sieve is weighed, recorded, and normalized to add up to 100%. then compares the percentage of each sieve to published standards such as; ANSI, FEPA, or custom specifications. Very fine particle sizes such as powders cannot be tested using a RoTap machine and sieves but rather on devices such as a Coulter Counter or a Micotrac to measure particle size distribution.
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