Short answer: An AS568 dash number fixes both the inside diameter (ID) and the cross-section (CS) of an O-ring. In the DuPont Kalrez AS-568 dimensions table, sizes -004 to -050 are 1.78 mm (.070 in) cross-section and the -1xx sizes are 2.62 mm (.103 in); Parker's ORD 5700 lists -214 at 3.53 mm (.139 in). Rings with almost the same ID can therefore be completely different parts. DuPont also notes that Kalrez compounds other than 4079, 1050, 1018 and 3018 may not conform to the listed dimensions because of differing shrinkage rates, so state the compound with the size.
1. Cross-section families
| Dash range (examples) | CS (in) | CS (mm) | Source |
|---|---|---|---|
| -004 to -050 | .070 | 1.78 | DuPont Kalrez AS-568 table |
| -102 to -179 | .103 | 2.62 | DuPont Kalrez AS-568 table |
| -214 | .139 ± .004 | 3.53 ± 0.10 | Parker ORD 5700, Section IX |
2. Three "25 mm" O-rings that do not interchange
All three would be described as "about 25 mm" on a purchase request. Their cross-sections differ by up to a factor of two, so each needs a different groove depth. A ring with the wrong CS will either not seal (too little squeeze) or overfill the groove. The groove decides the CS; the CS decides the dash series.
3. Compound affects dimensions too
DuPont's Kalrez AS-568 document states that the listed ring and cross-section dimensions apply to Kalrez parts, and that O-rings made from compounds other than 4079, 1050, 1018 and 3018 may not conform to the dimensions shown due to differing shrinkage rates. Semiconductor grades such as Kalrez 9300 or 9600 are not on that list, so when the fit is critical, ask for the actual molded dimensions of the grade you order. For choosing the grade itself, see [Kalrez 9100 vs 9300 vs 9500 vs 9600](/community/t/7-kalrez-9100-vs-9300-vs-9500-vs-9600-reading-dupont-s).
4. From an old ring to an orderable part
1. Find the dash number on the drawing, kit list or old bag label (Parker writes it as 2-214; AS568-214 is the same size).
2. Confirm the CS family against the groove: 1.78, 2.62 or 3.53 mm in the examples above.
3. Add compound and grade, for example Kalrez 9300.
4. If the grade is not one of the four compounds in DuPont's dimension note, ask for the molded dimensions.
5. No dash number: send ID × CS in mm with tolerance, how it was measured, and the tool-OEM part number with a photo. More fields are in the [FFKM O-ring RFQ guide](/community/t/12-how-to-write-an-ffkm-o-ring-rfq-that-actually-gets-quoted).
Kalrez is a trademark of DuPont. Parker is a trademark of Parker Hannifin. Names are used for identification only. MST is not affiliated with or endorsed by these companies.
Original OEM documents (links only)
1. DuPont, Kalrez perfluoroelastomer parts, O-rings AS-568 standard dimensions and metric equivalent. https://www.qnityelectronics.com/content/dam/electronics/amer/us/en/kalrez/public/documents/en/Kalrez_AS-568_Standard_O-rings.PDF
2. Parker Hannifin, Parker O-Ring Handbook ORD 5700 (Section IX sizes). https://www.parker.com/content/dam/Parker-com/Literature/O-Ring-Division-Literature/ORD-5700.pdf
Request a quote
Send the dash number (or ID × CS), compound and grade, process and quantity through a [sourcing RFQ](/services/sourcing-rfq?sourcing_mode=supplier_match), or post a [find-part request](/community/new?kind=part_request&mpn=AS568-214). Browse [semiconductor materials and consumables](/store/semiconductor-materials-consumables) in the store.