How to Measure an O-Ring
Measure O-ring inside diameter and cross-section, and understand metric and AS568 sizes.
An O-ring is normally specified by inside diameter (ID) and cross-section (CS), usually in millimetres or inches.
Use a suitable caliper and avoid stretching or excessively compressing the elastomer. Used rings may be swollen, flattened or permanently deformed.
Measure more than once, compare with the original groove dimensions and check the relevant metric or AS568 size series.
Correct sizing also requires groove design, squeeze, stretch, material, hardness and operating conditions. If uncertain, send the dimensions and a photo or drawing.
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