What’re the differences between Shore A, Shore M, Shore D, and IRHD?
These are four different methods of determine rubber hardness. All four evaluate hardness as the resistance to penetration of an indenter, but that’s where the similarities stop. Shore A is the most common method of evaluating rubber hardness in North America. Even though it’s a manual method, it has been shown to be very accurate and repeatable over the entire spectrum of materials and is not sensitive to the size or shape of the sample being tested, assuming proper measuring technique is used. Shore D is very similar to Shore A, but it’s intended for use with plastics. A Shore D measurement of 50 is approximately equal to a Shore A measurement of 90. Shore D is generally not valid for rubber O-rings. Shore M as designed specifically to measure finished O-rings. Because it removes the influence of operator technique, the results are more repeatable. However, Shore M results vary with the thickness of the O-ring being tested. A small cross-section O-ring could register as much as 20 po
