The durometer scale was defined by Albert Shore in the 1920's. He developed a device that could measure the hardness (resistance to permanent indentation) of a material.
There are many types of durometer scales for different kinds of materials, but most of our rubber products, including o-rings, fall under the “Shore A” or “Type A” category. Durometer is often referred to as “duro” for short. On the durometer scale, lower numbers represent a softer rubber. The hardness of the rubber increases as the durometer numbers go up. Our most commonly used durometers are 50 and 60, which are classified as a medium hardness.
Here is a general reference hardness chart to help choose the correct rubber durometer/hardness for your needs:
Material Comparison Examples
|40 Durometer||Soft pencil eraser|
|50 Durometer||Weather stripping for doors|
|60 Durometer||Auto tire tread|
|70 Durometer||Running shoe sole|
|80 Durometer||Leather belt|
|90 Durometer||Landline phone cord|