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:
Durometer |
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 |