Rubber hardness — measured as durometer — quietly determines whether your washer seals well, cushions well, or lasts. It's one of the most overlooked specs.
What durometer means
Durometer is measured on the Shore A scale for flexible rubber. Lower numbers are softer; higher numbers are firmer:
- 40-50 Shore A (soft): conforms easily, excellent sealing and cushioning on uneven or low-pressure surfaces
- 60-70 Shore A (medium): the all-purpose range — a balance of seal and durability
- 80+ Shore A (firm): resists extrusion and wear under high clamp loads, but seals less readily
How to choose
For sealing against irregular surfaces or at low torque, go softer. For high-pressure or high-torque joints where the washer must hold its shape, go firmer. For general use, medium hardness is the safe default.
Hardness works alongside thickness — see how the two interact in our size guide, and pick a compound in the material guide. Then shop by size.