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.
There are a number of brands of durometers, all of which
must conform to the same ASTM specifications if they are to be known as
genuine Durometers. Sometimes a Durometer Scale may be referred to by its'
brand name. The "A" scale is the Durometer A scale (or type A) and all
brands will, or should, give interchangeable readings.