sieve insert P-29 stainl.steel 6 mm square perforationSieve inserts determine the final fineness of a sample. Sieve inserts with trapezoidal and square perforations are offered. Sieve inserts with trapezoidal perforations improve size reduction through extra shearing action. Sieve inserts with square perforations are used for the grinding of brittle materials and materials of medium fineness with a narrow grain band.