Proportional Calipers

Product Files
Budget Proportional Caliper
Budget Proportional Caliper
Model: HM-38R
Price: $158.50
Four-Station Proportional Caliper
Four-Station Proportional Caliper
Model: HM-38B
Price: $174.50

Shape characteristics of coarse aggregates are important when determining the performance of materials or mixes. Proportional Calipers are timesaving devices used for rapid determination of percentages of flat and elongated particles in coarse aggregate fractions of 3/8in (9.5mm) or larger. 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, check 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 follows the same steps. If the particle is larger than the small measurement in both situations then the particle is considered neither flat nor elongated.

HM-38R Budget Caliper consists of a 6x16in (152x406mm) base plate with two fixed posts and a 13in (330mm) pivoting arm mounted between the posts so that there is an opening at each end of the arm. The pivoting arm adjusts by securing a pivot screw at one of four threaded positions to provide end opening ratios of 1:2, 1:3, 1:4, or 1:5.

HM-38B Four-Station Caliper is similar, but provides openings for all four ratios simultaneously, without the need to reposition the pivot screw. Manual testing can be performed more efficiently. Moveable posts are also replaceable.


  • Time-saving way to determine percentages of flat or elongated particles in coarse aggregate
  • Meet requirements of ASTM D4791
  • Optimal for fractions of 3/8in (9.5mm) or larger
  • Sturdy aluminum body is precision-tooled for accuracy

Included Items:

  • HM-38R Budget Caliper


  • HM-38B Four Station Caliper
Dimensions 16x6x3in (406x173x76mm), WxDxH
Estimated Shipping Weight 16lb (7kg)
Dimensions 16x8x3in (406x203x76mm), WxDxH
Estimated Shipping Weight 16lb (7kg)

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