O-Ring Groove Identifier — Reverse Engineering Tool

How to Measure an Existing Groove

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

• 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.
• Groove Width: Use calipers or a groove gauge. Measure the width of the channel the o-ring sits in.
• 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 cross-section (CS) is most reliable; the ID will be stretched from service, and CS 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 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 (JIS B 2401, ISO 3601).
• Custom sizes — some OEMs use proprietary o-ring sizes.
• Quad rings / X-rings — four-lobed seals that use different groove geometry.