What are inside diameter, cross-section and outside diameter?
- Inside diameter: The diameter of the opening at the centre of the O-Ring.
- Cross-section: The circular thickness of the ring body.
- Outside diameter: The overall outside-to-outside diameter of the O-Ring.
O-Rings are primarily identified by inside diameter and cross-section together. Outside diameter can help check the consistency of the measurement.
How is an O-Ring measured?
- Place the O-Ring on a clean, flat surface without stretching it.
- Measure the diameter of the inner opening without extending the product.
- Check the thickness of the ring body at several points.
- Record the size as “inside diameter × cross-section” together with the unit.
- If a used product appears compressed, stretched or swollen, also provide the groove dimensions.
Points to consider
- Do not measure the O-Ring while pulling or stretching it.
- Do not measure the cross-section at only one compressed point.
- Always state whether the unit is millimetres or inches.
- Do not identify the material solely by colour.
- Remember that groove and operating conditions may be evaluated differently in static and dynamic applications.
Material selection depends on the fluid and operating conditions. A product should not be selected on the basis of unverified temperature, pressure or chemical resistance assumptions.
Frequently Asked Questions
How is O-Ring size specified?
Inside diameter and cross-section are generally specified together. Clearly stating the dimension order and unit makes product matching easier.
Can a used O-Ring be measured?
Yes, but because it may be stretched, compressed or swollen, the result should be verified against the groove dimensions and a new sample whenever possible.
Can O-Ring material be identified by colour?
Colour alone is not a reliable method of identifying a material. Product code, supply information and application conditions should be evaluated together.
Related Products
O-RINGS
KO O-Rings
View product →MAINTENANCE & SERVICE
O-Ring Kits
View product →CONTINUOUS LENGTH
O-Ring Cord / Extruded O-Ring Cord
View product →Related Technical Guides
Let us verify your O-Ring size together.
Send your dimensions, groove information, sample or photographs to our technical team.