Rubber hardness is expressed on the Shore A scale, and is measured with a durometer. The number may be specified as “60 Shore A”, or commonly as “60 durometer”. The number, itself, signifies the relative hardness within the A scale. Typically, the hardness of calendered rubber sheet ranges from 40A (soft) to 90A (very hard) in 10 point increments. Hardnesses below 40A are also available, though these sheets might be molded rather than calendered.
The most common rubber gasket hardness for Neoprene, Nitrile, and EPDM compounds fabricated from sheet is 60A, though softer and harder grades are also available. Red SBR (red rubber) is generally 75-80A, and Viton is typically 75A. Molded rubber products are available in hardnesses from 20A to 90A. O-ring hardness is usually 70A and, as with all rubber products, options are available.
All hardnesses have a tolerance of +/- 5 points. This means a 70A rubber can measure 65A, and a 60A rubber can also measure 65A; both would be acceptable. Because of the tolerance, it might be advisable to consider at least 20 point changes when testing the effect of particular hardnesses.
Please contact Expert Gasket & Seal with questions regarding rubber hardness for your rubber gasket, rubber seals, or rubber o-ring applications.