U.S. Standard Sieve Sizes

U.S. standard mesh or sieve numbers, widely used in geological particle sizing, are arbitrary designations and do not refer to actual mesh count. They are the open width of one side of the square aperture and are made to micron sizes, not English measurements, using heavy wire woven with square holes. The standard sieve for freshwater, estuarine and marine benthic macroinvertebrates is # 35.