Shape characteristics of coarse aggregates are important to performance of materials or mixes. HM-38R and HM-38B Proportional Calipers are timesaving devices. Use either for rapid determination of percentages of flat and elongated particles in coarse aggregate fractions of 3/8in (9.5mm) or larger. Both units are constructed of durable aluminum, precision tooled for accuracy.

For shape determination of flat particle sizing, set the width of a particle in the larger end of the Caliper, then tighten the pivot screw. Without adjusting the Caliper, determine the thickness of the same particle in the smaller measuring end of the Caliper. If the particle fits within the smaller gap, it is considered flat. Elongated particle determination uses the same steps. If the particle is larger than the small measurement in both situations then the particle is considered neither flat nor elongated.