The NIST Glass Beads for Sieves, #25 to #60, are calibrated glass beads for determining effective sieve opening. (NOT for determining conformity to specifications.) They are also useful for calibration of electroformed sieves. The entire sample is placed on clean sieves and shaken in the manner that tests will be made on test samples.
Percent of glass beads retained on each sieve is calculated, and effective opening of each of the sieves is determined from calibration data on the NIST Certificate supplied with the bead set.