Backup Ring Size Chart
AS568 back-up ring size chart: dash numbers with ID, width, height, and contour dimensions for high-pressure extrusion protection.
Back-up rings (anti-extrusion rings) sit beside an O-Ring to block the clearance gap under
high pressure. This chart lists AS568 dash sizes with contoured-style dimensions:
ID, radial width (W), axial height (HT), and contour geometry. Dash numbers
match the companion O-Ring (e.g. AS568-214 backup fits an AS568-214 O-Ring).
Prefer the interactive filter on the Master O-Ring Size Chart — select the AS568 Backup standard chip to switch headers to full back-up dimensions.
How to use this chart: enter the O-Ring dash in Code / dash, or search by W and ID. Nearest matches sort to the top. On phones or a slim browser window, sizes switch to a card view (use the unit toggle for inch, mm, or both); the wide table returns on larger screens. Code links open a product search on theoringstore.com.
For O-Ring dash numbers and cross-section series, see Sizing & Standards.
| Code | Series | ID (in) | W (in) | HT (in) | Contour R (in) | Contour HT (in) | ID (mm) | W (mm) | HT (mm) | Contour R (mm) | Contour HT (mm) |
|---|---|---|---|---|---|---|---|---|---|---|---|
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Default sort is dash / catalog order (AS568-004…475). Click a column header to re-sort. W is radial width; HT is axial height; contour columns apply to contoured (dished) styles. W/ID search ranks nearest matches first. Dash numbers match the companion AS568 O-Ring size. Dimensions from The O-Ring Store contoured back-up ring chart — confirm with the controlling drawing for critical fits. Code links open a product search on theoringstore.com.
When to use a back-up ring
Use one or two back-up rings when:
- System pressure is roughly above 1,500 psi, or the extrusion gap is large
- Temperature softens the O-Ring and increases extrusion risk
- You need longer seal life without tightening hardware clearances
Pressure direction: one ring on the low-pressure side for unidirectional pressure; two rings (one on each side) for bidirectional or unknown pressure.
Gland width must be wider than a standard O-Ring groove to fit one or two backups plus the O-Ring. Always confirm groove design against the application drawing.
Styles available
| Style | Typical materials | Notes |
|---|---|---|
| Contoured (dished) | Buna-N 90, FKM 90 | Concave face mates to the O-Ring; stretch-to-install elastomer |
| Solid (uncut) PTFE | PTFE / Teflon® | Highest chemical & extrusion resistance; harder to install on closed grooves |
| Split / scarf-cut PTFE | PTFE | Easier install; single-turn cut |
| TPE (Hytrel®) | Thermoplastic polyester elastomer ~55D | Tough, abrasion-resistant; good for hydraulics & water-based fluids |
Shop: Back-Up Rings · Solid PTFE · Split PTFE · TPE Hytrel · Contoured Buna-N · Contoured FKM
