O-Ring Groove Design: Gland Dimensions by Cross-Section

An O-ring groove is sized from three numbers: the cross-section of the ring, the squeeze the seal type needs, and the free volume the ring must have to swell and expand into. For a static face seal in liquid service the published manufacturer tables put squeeze at roughly 19 to 32 percent on the smallest AS568 section and 21 to 29 percent on the largest, with gland fill held between 60 and 85 percent of groove volume (Parker's handbook gives 75 percent as the optimum). This guide tabulates the groove width and depth for every AS568 family across the three common gland types, from the Parker ORD 5700 lineage that the AS568 industrial tables descend from, cross-checked against ERIKS, Trelleborg and Precision Associates, and explains the rules that sit behind the numbers.

Which gland type, and which convention?

Three gland types cover most O-ring seals: the static face (axial) seal, where the ring is squeezed between two flat flanges; the static radial seal, where a piston or rod carries the ring into a bore or tube without motion; and the dynamic reciprocating seal, where the rod or piston moves. Squeeze falls from face to radial to dynamic, because motion adds friction and wear. Two conventions publish dimensions: the AS568 industrial tables (Parker and MIL-G-5514 lineage, carried by SAE AS4716 and AS5857) and ISO 3601-2 for metric hardware. They disagree slightly on static gland depth for the large sections, so a calculation should use one convention and say which. All tables below are the AS568 industrial convention in inches.

Static face seal groove dimensions (liquid service)

Internal and external pressure share the same groove; only the stretch rule differs (ring stretched 0 to 2 percent for internal pressure, 1 to 3 percent for external, per the Parker lineage tables). Vacuum and gas service uses a narrower groove, listed in the last column, so the fill runs higher.

Which groove diameter is sized to the ring depends on the pressure direction: Precision Associates sizes the groove outside diameter to the ring outside diameter plus the ring's tolerance, and Trelleborg keeps the ring outside diameter equal to, or at most 1 to 2 percent larger than, the outer groove diameter. ERIKS notes that the no-extrusion-gap argument for a face seal holds only while the flanges stay in metal-to-metal contact and do not deflect under pressure.

Static radial and dynamic reciprocating groove dimensions

Radial glands share groove widths; the depth and the squeeze change with the duty. Trelleborg allows piston seals 2 to 8 percent stretch (static) or 2 to 5 percent (dynamic); Parker does not recommend more than 5 percent, and above 2 to 3 percent it calls for a gland-depth correction. Rod seals sit at zero stretch. Groove width figures are for a plain O-ring; widen the groove by the thickness of each backup ring when one is used (ERIKS).

Rotary service is its own design case: the ring is sized larger than the shaft, not smaller, so that it does not shrink onto the shaft and overheat, and the Parker handbook discourages plain O-rings as rotary seals beyond low speeds. Note that the squeeze percentage falls as the section grows, by design (ERIKS): one percentage across all five families is wrong. The squeeze guide explains the bands and what temperature and swell do to them.

Gland fill: the rule that catches the tolerance stack

Fill is the ring's cross-sectional area divided by the groove's width times depth, where the ring area is pi over four times the cross-section squared. Parker's handbook band is 60 to 85 percent with 75 percent optimum; Trelleborg's ceiling is 85 percent; Marco Rubber cites 75 percent nominal; Apple Rubber allows the ring volume up to 90 percent of the minimum gland void, and 95 percent for a static crush seal only. The void exists because thermal expansion, fluid swell and the tolerance stack all need somewhere to go. Evaluate fill at the worst case, maximum ring section against minimum groove width and depth: a gland that reads 80 percent at nominal can read 90 percent at the extremes. ERIKS' sizing rule for a swelling fluid is groove volume equal to ring volume times one plus the chemical swell plus the thermal expansion, times 1.2.

Surface finish and edges

Two cautions from the literature. RMS and Ra are not the same measure, but the seal makers use them interchangeably at these magnitudes; treat a 32 RMS and a 32 microinch Ra callout as the same requirement and never convert between them. And the number alone is incomplete: ERIKS points out that a lathe-turned groove at 125 RMS can outseal an end-milled one at 63 RMS, because turning marks run with the ring and milling scratches cut across it. Groove corners take the radius in the first table; the gland entry gets a chamfer so the ring is not cut on installation.

Dovetail and backup-ring grooves

A dovetail groove holds the ring in a face seal for maintenance (vacuum chambers, lids that open). ERIKS and Trelleborg recommend it for the 0.139 in section and larger, call it expensive, and note that its trapezoid section makes the rectangular fill formula overstate the free volume. ERIKS' table still lists the smaller sections: its dovetail squeeze runs 27 percent on the 0.070 section down to 16 percent on the 0.275 section, with groove openings of 0.055 to 0.059 in and 0.231 to 0.235 in respectively. When pressure exceeds what the plain groove can hold, a backup ring goes on the low-pressure side and the groove widens by its thickness; ERIKS' widths for a 0.139 in ring run 0.204 to 0.209 in with one rubber backup and 0.271 to 0.276 in with two. The durometer guide carries the pressure-versus-clearance figures that decide when a backup ring is needed.

The ranges in this guide are the published design guidelines of the manufacturers named beside them (Parker, ERIKS, Trelleborg, Precision Associates, Marco Rubber, Apple Rubber), re-arranged by seal type and AS568 cross-section family. They are not Conquest Seal engineering recommendations: Conquest distributes seals and cuts gaskets, and does not design parts. If a drawing calls out SAE AS4716, SAE AS5857, ISO 3601-2 or MIL-G-5514, the standard governs and these ranges are context.

Sources

1. Parker O-Ring Handbook ORD 5700A/US, sections 3.5 to 3.7 (stretch, squeeze and gland fill), read 2026-08-12
2. AS568 industrial gland tables (Parker and MIL-G-5514 lineage), cross-checked against the manufacturer guides below, read 2026-09-06
3. ERIKS nv, O-ring Technical Handbook, chapter 12, O-ring Gland Design, read 2026-09-06
4. Trelleborg Sealing Solutions, O-Rings and Back-up Rings catalog (June 2024 edition), read 2026-09-06
5. Precision Associates, Application Data: Seal Gland Design (2011), read 2026-09-06
6. Marco Rubber (Marco Sealing Solutions), Understanding O-Ring Squeeze, Stretch and Compression, read 2026-09-06
7. Apple Rubber Products, Seal Design Guide (Rules of Thumb; O-Ring Installation), read 2026-09-06
8. SAE AS4716 and AS5857, ISO 3601-2 and MIL-G-5514: titles and scope only, from the SAE, ISO and ASSIST records read 2026-09-06

Reviewed by Grant Midstokke, Conquest Seal Corporation. Last updated September 2026. Spec values in this guide are drawn from the sources listed above; the compound datasheet and your application conditions govern the final choice.