Instruments as per ASTM D2240
Standard Test Method for Rubber Property—Durometer Hardness
The standard test method covers twelve types of rubber hardness measurement instruments known as durometers namely, Durometer Type A, B, C, D, DO, E, M, O, OO, OOO, OOO-S and R. The method for determining the indentation hardness of substances classified as thermoplastic elastomers, elastomeric materials, vulcanized rubber, gel-like materials, cellular materials and some plastic materials also.
This test method work on the basis of the penetration of a particular type of indentor when forced into the product under various conditions. The indentation stiffness is inversely related to the penetration and is reliant on the elastic modulus and visco elastic behavior of the product. The indentor’s geometry and the exerted strength manipulate the measurements so that no simple correlation exists between the measurements obtained with one type of durometer and those obtained with another type of durometer or other measuring instruments used for measuring hardness. This standard method is an empirical test intended primarily for control purposes.