About O-Ring Finder

A free reference for identifying AS568 o-rings from measurements. No accounts, no quote forms, no signup.

What this is

O-Ring Finder does one thing: you measure a ring, it tells you the AS568 dash number. It covers all 361 sizes in the standard series, with dimensions in both millimetres and inches.

The reason it exists is that the data is everywhere and the tool is not. Search for o-ring sizes and you get static charts — PDFs and tables that assume you will scan several hundred rows by eye. That works badly when what you have is a measurement rather than a part number, and it works especially badly when the ring you measured has shrunk in service, which is the normal case.

Who publishes it

O-Ring Finder is an independently operated reference site. It is not affiliated with, endorsed by or sponsored by any seal manufacturer or distributor, and it does not sell o-rings. There is no quote form and no commercial relationship with any supplier.

The site is funded by display advertising. Advertising has no influence on the dimensional data. See the privacy policy for how advertising works here.

Where the numbers come from

Dimensions are the SAE AS568 standard series. Inch dimensions are stored as published; millimetre figures are computed from them rather than copied, because published millimetre columns frequently disagree with their own inch columns on the largest sizes. Several widely reproduced charts list dash 282 as 405.26 mm when 15.984″ converts to 405.99 mm, and repeat the same drift on 283, 284, 385, 386 and 387. Deriving from a single authoritative column removes that whole class of transcription error.

Every size is checked at build time: inside diameter must increase with dash number within each series, and outside diameter must equal inside diameter plus twice the cross section. If a check fails, the site is not published.

Limitations

Corrections and requests: get in touch.