Sieves are made of suitable materials with square openings. For purposes other than analytical procedures, circular sieves may also be used; in this case, the internal diameters of circular sieves should be 1.25 times the square opening size of the corresponding sieve size. There should be no reaction between the sieve material and the material being sieved.

The degree of grinding is determined using the sieve number. The sieve number is the measurement of the opening size in micrometers, specified in parentheses next to the name of the substance.

The maximum tolerance for an opening (+X) indicates that the opening should not exceed the nominal size by more than +X:

X = \( \frac{2 \left(w^{0.75}\right)}{3} + 4 \left(w^{0.25}\right) \)

Here, \(w\) is the width of the opening.

The tolerance for mean opening (±Y) allows a deviation of ±Y from the nominal size of the opening:

Y = \( \frac{w^{0.88}}{27} + 1.6 \)

The intermediary tolerance (+Z) states that no more than 6% of the total number of openings should be between "nominal +X" and "nominal +Z":

Z = \( \frac{X + Y}{2} \)

Wire Diameters: Wire diameter \(d\) values are mounted in frames with woven metal wire cloth. The nominal sizes of wire diameters may deviate within the limits of \(d_{\text{max}}\) and \(d_{\text{min}}\) specified in the table. The permissible tolerance for choice is set at 15% of the nominal sizes. In cast sieves, wires should have similar diameters in both warp and weft directions.

Values in Micrometers