I.R.H.D. (International Rubber Hardness Degrees)

A system of defining an elastomer by its resistance to penetration of a known geometry indenter by a known force.
The micro-technique is reproducible on irregular as well as flat surfaces and on cross-sections as small as 1mm in thickness (.04″). Measurements taken using the IRHD scale are similar, but not identical, to those obtained using the Shore A scale.