The X-ring, also called a quad ring, looks like an O-ring that grew four lobes. It installs into the same standard AS568 or metric grooves, costs a little more, and solves two problems that have plagued dynamic O-ring seals for decades: friction and spiral failure. This article explains when the four-lobed profile earns its premium and when a conventional O-ring remains the rational choice.
A conventional O-ring seals through one broad contact band created by squeezing a round cord. An X-ring presents two sealing lips on each side of the cross-section, separated by a lubrication-retaining groove. Its mold parting line sits in the valley between lobes — away from the contact surface — instead of across the sealing face.
| Factor | O-Ring | X-Ring (Quad Ring) |
|---|---|---|
| Contact with hardware | One wide contact band | Two narrow lip contacts per side |
| Friction in motion | Higher; prone to stick-slip at low speed | Significantly lower; smoother start-up |
| Spiral (twist) failure | Common in reciprocating service when lubrication is poor | Resists rolling — the lobes index the ring in the groove |
| Required squeeze | Standard 15–25% depending on seal type | Lower (often roughly half in dynamic grooves) |
| Parting line on sealing surface | Possible flash on the contact face | Parting line is in the non-contacting valley |
| Lubrication | Squeeze wipes film away | Central grooves retain a lubricant reservoir |
| Groove compatibility | Standard AS568 / metric grooves | Fits the same grooves in most static/dynamic designs |
| Cost & availability | Lowest cost, universally stocked | Somewhat higher cost, fewer compounds stocked |
For purely static duties the X-ring's friction and anti-roll advantages are irrelevant; the O-ring is cheaper, available in more compounds and colors, and seals identically. X-rings are also stocked in a narrower material range (NBR and FKM are easy to source; specialty compounds may be custom-only), and in very small sizes the four-lobed geometry becomes hard to mold consistently. Finally, always confirm the groove chart for your chosen brand — the squeeze recommendations differ, and installing an X-ring to O-ring squeeze percentages over-compresses it.
Because X-rings use the same nominal cross-sections (1.78 / 2.62 / 3.53 / 5.33 / 6.99 mm), converting an existing design is normally a direct one-for-one swap using the same dash or metric size — no hardware change. The two things to re-check are the dynamic squeeze percentage against the X-ring manufacturer's groove table and lubrication at assembly.
Think of the X-ring as an O-ring optimized for motion: same groove, same materials, but engineered to stop rolling and to slide. If the seal never moves, you are paying for capability you will not use.
We supply X-rings in NBR and FKM across standard AS568 and metric sizes. See the Rubber Ring product category for the full range, or contact us with your groove dimensions and motion parameters for a direct O-ring → X-ring cross-reference.