Rex Gauge Durometers
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Rex Gauge Durometers - Space Certified Technology

Technical Information

Rex Gauge Durometers

Rex Durometers are known World-Wide for their quality, dependability and accuracy. Except where noted, all gauges comply with ASTM D2240. All are in stock and ready for immediate delivery. Custom designed gauges and operating stands, along with many accessories are available.

What is a Durometer

The Durometer is the international standard for the hardness measurement of rubber, plastic and other non-metallic materials. Durometers are described in the American Society for Testing and Material specification ASTM D2240, which is the recognized specification for the instrument and test procedures.

Reference Checking

To make a simple operation check, take a reading on smooth glass or steel (WARNING: THIS IS NOT RECOMMENDED FOR TYPE D DUROMETERS-THE GAUGE MAY BE SEVERELY DAMAGED). The gauge should read no more than 100 and no less than 99. In a Rex Durometer, the unique built-in linearity assures the gauge is in proper operation throughout the entire scale. Should a Rex Durometer not give the above reading on a smooth, hard surface, it may be assumed that the Durometer has been damaged, and it should be sent to Rex for inspection and/or repair.

Durometer Test Blocks give the user the ability to develop the proper "feel". Test Blocks are not to be used for calibration purposes, however it does enable the user to perform a quick check for proper durometer operation.

Testing Procedures

Durometers measure hardness by relating the penetration of an indentor into a specimen, and because the indentor travel may reach .100", it follows that a specimen must be of sufficient thickness to ensure a proper, sensitive test. Generally, samples to be tested should not be less than 1/4" (6mm) thick. Exceptions may be made for harder materials because the indentor is at less than half stroke. What must be avoided is a specimen so thin that the indentor may sense the hardness of the underlying surface. This will give a false reading due to the "anvil effect". The Rex Type M durometer can be used when checking materials thinner than 1/4" (as thin as .050").

When testing flat specimens too thin to give accurate readings, the specimens may be stacked to provide the required thickness.

In addition to sufficient thickness for testing, sufficient material around the sides of the indentor must be present. With soft materials, a minimum 1/4" (6mm) is recommended.

Reference Guide

Type Application Indentor Spring Force
A Rubber, Elastomers Flat Cone Point 35° Type A Indentor 822 g
B Harder Elastomers, Plastics, Paper, Fibrous Materials
Use above 93 A scale.
Sharp Cone Point 30° Type B Indentor 822 g
C Medium Hard Elastomers, Plastics.
Useful to avoid surface marks.
Flat Cone Point 35° Type C Indentor 10 lb
D Hard Rubber, Plastics, Thermo Plastics Sharp Cone Point 30° Type D Indentor 10 lb
DO Dense Granular Materials, Textile Windings 3/32" Spherical Type DO Indentor 10 lb
O Very Soft Elastomers, Textile Windings, Soft Granular Materials Use below 20 A scale. 3/32" Spherical Type O Indentor 822 g
OO Foams, Sponge Rubber, Gels, Animal Tissue. 3/32" Spherical Type OO Indentor 113 g
OOO Open Cell Foams, Ultra-soft Gels, Sponge Rubber. 1/2" Spherical Type OOO Indentor 113 g
M Rubber, Elastomers
Materials as thin as .050"
Sharp Cone Point 30° Type M Indentor 78 g

Comparison Chart

Note: This chart is for comparison purposes only.

Comparison Chart
Comparison Chart

Durometer Selection Guide