Elastomer durometer describes a rubber-like material's resistance to indentation on a stated hardness scale. A calibrated indenter presses into the specimen and the instrument reports a value. The scale, test conditions and specimen matter; a hardness number alone does not identify a suitable replacement seal.
Elastomer durometer describes a rubber-like material's resistance to indentation on a stated hardness scale. A calibrated indenter presses into the specimen and the instrument reports a value. The scale, test conditions and specimen matter; a hardness number alone does not identify a suitable replacement seal.
Keep the scale with the number
Parker's O-Ring Handbook describes Shore A as a commonly used scale for sealing elastomers. It also explains that other scales and hardness methods exist. A number copied without its scale loses information needed to interpret it.
Apple Rubber's measurement article shows why a small curved O-ring and a suitably prepared flat specimen are different measurement situations. Specimen thickness, geometry and the material beneath the specimen can affect the reading. Its discussion distinguishes Shore A from a micro-hardness method rather than treating their results as automatically interchangeable.
A fingernail impression or the feel of an old gasket is not the documented test. Ask which scale and method the part specification actually requires before comparing values from different data sheets.
Hardness is one part of seal selection
Charlotte Pipe's flange instructions specify a gasket arrangement and a Shore A hardness range within that particular plastic-piping application. That example does not establish the right hardness for a faucet seal, a tubular drain washer or every other pipe flange.
Material formulation, dimensions, fluid compatibility, temperature and the joint's design remain separate requirements. A matching hardness number does not establish drinking-water approval, chemical resistance or the installed assembly's pressure rating.
Hardness also differs from compression set, which describes residual deformation after a specified compression-and-recovery test. One property should not be used as a substitute for the other.
Read the complete replacement specification
Keep the manufacturer's part identification, material designation, dimensions, hardness scale and any stated test method together. Where a seal is supplied as part of an identified fitting system, use that system's compatible replacement instructions.
Our grooved coupling entry explains why gasket application belongs to the complete joint. Color and apparent softness cannot confirm that an unmarked ring meets those requirements.
If an old part has changed shape, cracked or deteriorated, have the affected assembly assessed. Do not select a replacement simply by reproducing the feel of the worn material or trying to compensate by tightening the joint further.