What is the Durometer of an O-Ring?

Durometer is the international standard for measuring the hardness of objects like rubber and plastic. There are a few different measurement scales, call Shores. There is Shore 00, Shore A, Shore D and others as well. The Shore A type durometer scale is generally used to measure the hardness of most rubber compounds. Rocket Seals uses the Shore A scale. Normally, durometer hardness is referred to in increments of five or ten, such as 50 durometer, 70 durometer, 75 durometer, etc.

O-Rings are available in almost all durometers, with 70 or 90 durometer, the most common in most compounds.

Softer sealing materials, with lower hardness readings, will more easily flow into the microfine grooves and imperfections of the mating parts, but softer compounds, like 50 durometer compounds, wear and extrude very quickly

Harder materials, like 70, 75 or 90 durometer compounds, offer greater resistance to extrusion. In dynamic applications, the hardness of the O-Ring is doubly important because it also affects both breakout and running friction.

For most applications, compounds having a durometer hardness of 70 to 90 is the most suitable compromise.