How to Specify an O Ring Without Mixing Up Its Dimensions
For a conventional circular O-ring, state the inside diameter and cross-section, then give the units. Add the material specification and any applicable size reference. A number such as “20 by 2” is clearer when written as “20 mm inside diameter by 2 mm cross-section.” This is an illustrative notation example, not a product recommendation.
Which dimension is which
Inside diameter, or ID, describes the opening. Cross-section, or CS, describes the thickness of the circular rubber section. For ideal circular geometry, the outside diameter equals the inside diameter plus twice the cross-section. Label the dimensions explicitly so the recipient does not have to infer whether a quoted diameter is ID or OD.
IKSONIC’s O-ring information and size references page is a starting point for reviewing the available size-reference information.
Should I measure a used O ring
Treat an old part as evidence to be checked. Service exposure can leave a flattened section or change the rubber’s size. Record whether measurements came from a new part, a used part, a drawing or the housing. If the evidence disagrees, ask for a specification review instead of silently choosing the closest catalogue entry.
Can I substitute a nearby metric or inch size
Do not approve a substitution from rounded numbers alone. Give the applicable standard or catalogue reference when known, and keep the original units. Ask the supplier to confirm the nominal dimensions, tolerances and housing requirements. A close numerical match is a candidate for review, not proof of equivalent sealing performance.
What should an O ring inquiry contain
- ID and cross-section, units and the source of the dimensions
- Standard or size reference when known, plus required tolerances
- Compound or material requirement and hardness specification, if already defined
- Medium, concentration, temperatures, pressure conditions and static or moving service
- Quantity and required documentation, with unknown items clearly marked
Keep dimensional identification separate from material qualification. An O-ring can have the right nominal size while its compound still needs application review. The related product information below does not select a material for your equipment.
Related product information
HNBR O-ring product information
Use these listings to discuss product options. Confirm the exact specification and application suitability before ordering.
Contact IKSONIC with the completed size description and operating conditions. Share only the drawings and specifications you are authorized to provide.