O-Ring Identifier — Find the Right O-Ring from Groove Measurements

O-Ring Seal Types — Shaft, Piston, and Face Seal cross-section with groove dimensions

Groove dimension reference — Shaft (Rod), Piston, and Face seal applications

O-Ring Identifier — Find the Right O-Ring from Existing Groove Dimensions

Got a piece of equipment with a worn, rotted, or missing o-ring? Measure the groove and this tool will tell you which standard AS568 o-ring to order — ranked by how well each size fits your existing geometry.

Seal Type
Groove ID (inches)
Groove Depth (inches)
Groove Width (inches)

How to Measure an Existing Groove

  1. Groove Depth: Use a depth micrometer or pin gauge. Measure from the sealing surface down to the bottom of the groove. If the groove is worn, measure in the cleanest area.
  2. Groove Width: Use calipers or a groove gauge. Measure the width of the channel the o-ring sits in.
  3. Groove Diameter: For face seals, measure the groove ID (inner wall of the circular groove). For piston seals, measure the bottom of the groove. For rod seals, measure the bore groove OD.

Tips for Worn or Corroded Grooves

  • If the groove is corroded, the original dimensions may be slightly larger (depth) or wider. Measure the cleanest section and note that the original groove was slightly tighter.
  • If you have the old o-ring (even damaged), measure it. The CS is most reliable — ID will be stretched from service. Cross-section narrows which series to look at.
  • If multiple o-rings match well, pick the one with higher squeeze (up to 25%) for a more positive seal. This compensates for any groove wear.

What If Nothing Matches?

If no standard AS568 o-ring fits well, the groove may have been designed for:

  • Metric o-rings — common in European and Japanese equipment. Metric o-rings use different size standards (JIS B 2401, ISO 3601).
  • Custom sizes — some OEMs use proprietary o-ring sizes.
  • Quad rings or X-rings — four-lobed seals that use different groove geometry.

Understanding the Results

  • Green = parameter is within ideal range (Squeeze 15–25%, Fill 75–85%, Stretch 0–5%)
  • Yellow = borderline — will probably work but not optimal
  • Red = outside recommended range — not recommended

The tool ranks all 250+ standard AS568 o-ring sizes and shows you the best matches. The top-ranked o-ring gives you the closest to ideal squeeze, fill, and stretch for your measured groove.

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