O-ring references use several designation systems, and their scopes do not line up as a single universal code. SAE AS568 identifies aerospace O-ring sizes by dash number and specifies inside diameter, cross-section, and tolerances. ISO 3601 is divided into separate parts: one for ring dimensions and designation codes, another for housing dimensions, and another for quality acceptance. This cross-reference shows which document answers which question; it does not reproduce any standards table.

O-Ring Size and Designation Standards

Choose the part that matches the lookup

Start by deciding whether the drawing calls out an O-ring size, a groove, or an acceptance criterion. For a size designation, check AS568F or ISO 3601-1 as applicable. The SAE catalogue says AS568F covers inside diameters, cross-sections, tolerances, and size identification codes. ISO lists ISO 3601-1:2012 with its 2019 amendment for inside diameters, cross-sections, tolerances, and designation codes in general industrial and aerospace fluid-power systems. These documents may describe similar concepts, but an identifier from one system should not be converted by guesswork into another code family.

Do not mix a ring size with a groove

A ring’s nominal dimensions and the cavity that holds it are different parts of the design. ISO 3601-2:2025 addresses housing dimensions for general applications. Its subject is the groove or housing rather than the code used to identify a ring. Groove dimensions depend on whether the seal is static or dynamic, the direction of pressure, the material’s deformation, and the design’s tolerances. A size code by itself cannot establish squeeze, stretch, extrusion clearance, or gland fill. Use the current design standard and manufacturer guidance for the actual application.

Quality criteria are a separate question

ISO 3601-3 covers quality acceptance criteria. That is not interchangeable with sizing or groove design. Inspection requirements can include matters that a part number does not encode, and acceptance limits should be taken from the standard and procurement specification that control the order. Record the standard and revision in the drawing or purchase documentation instead of relying on a supplier’s shorthand when the requirement is critical.

Compound compatibility is outside the size code

An O-ring can have the right nominal size and still be unsuitable. The material compound, hardness, fluid, temperature, pressure, motion, surface finish, and exposure time all affect sealing behavior. A dash number is not a polymer name or a pressure rating. Confirm the compound and its compatibility with the fluid, including cleaning agents and mixtures that may appear during maintenance. Review low-temperature recovery and high-temperature aging where they matter. Ask the seal supplier to confirm a design when unusual media, vacuum, motion, or safety requirements are involved.

How to read a cross-reference safely

Use this table to locate the governing document, then read the relevant edition rather than treating a summary as a substitute. A manufacturer handbook may explain how systems are commonly encountered, but it can predate a later standard revision. ISO currently lists ISO 3601-2:2025, while ISO 3601-1 remains the 2012 edition with a 2019 amendment and ISO 3601-3 is listed with its 2018 amendment. SAE lists AS568F as current. Verify these editions again when a design is released or a controlled drawing is updated.

If a supplier offers a cross-reference, check whether it covers the exact standard, size range, tolerance class, and material requested. “Equivalent” may mean the nominal cross-section is close, not that every tolerance and groove requirement matches. Retain the source standard and supplier confirmation with the design record so a later replacement does not silently change the interface. For pressure-containing or safety-critical equipment, have the complete seal and gland reviewed by a qualified engineer.

References

• SAE AS568F, Aerospace Size Standard for O-Rings
• ISO catalogue: O-ring standards
• Parker O-Ring Handbook

This reference describes selected standard scopes only. Confirm the controlling edition, seal compound, groove design, tolerances, and actual service conditions before selecting or approving an O-ring.