AS568 O-Ring Groove Dimensions Chart & Gland Calculator (Face & Piston)
Under SAE AS568, ISO 3601-2, and the Parker O-Ring Handbook (ORD 5700), a standard elastomeric O-ring gland must be machined to a groove depth that compresses the cross-section by 20% to 30% for static seals (or 10% to 18% for dynamic piston/rod seals) while sizing groove width so cross-sectional gland fill remains between 70% and 85%.
⭕ Interactive SAE AS568 O-Ring Groove Depth, Width, % Squeeze & % Gland Fill Calculator
Select your AS568 cross-section series (-0xx to -4xx), sealing application (Static Face, Dynamic Piston, or Rod), and backup ring count per Parker O-Ring Handbook (ORD 5700).
How Do SAE AS568 Cross-Section Series (-0xx to -4xx) Govern Groove Depth and Width?
Every standard aerospace and industrial O-ring specified under SAE AS568D, ISO International Metrology Standard (ISO 3601), and ASME Geometric & Mechanical Standards fluid power standards is grouped into one of five standard cross-section thickness series identified by the first digit of its 3-digit Dash Number: the -0xx series (nominal 1/16", actual cross-section CS = 0.070" ± 0.003"), -1xx series (3/32", CS = 0.103"), -2xx series (1/8", CS = 0.139"), -3xx series (3/16", CS = 0.210"), and -4xx series (1/4", CS = 0.275"). Because sealing force depends entirely on the radial or axial compression of that toroidal cross-section, all O-ring dash numbers within the same series share the exact same groove depth and groove width!
When CNC milling a rectangular gland groove, two dimensionless engineering ratios must be verified simultaneously: Compression Squeeze % [(CS - Depth) / CS] × 100 and Gland Fill % [π × (CS / 2)² / (Depth × Width)] × 100. If Gland Fill exceeds 85% to 90%, thermal expansion of the nitrile (NBR) or Viton (FKM) elastomer—which expands at 10× the rate of the steel housing—will overfill the rectangular cavity and extrude the rubber into the diametral clearance gap, shearing the seal! Check housing bore fits on our ISO 286 Hole & Shaft Tolerance Calculator.
| AS568 Dash Series | Nominal Fraction CS | Actual CS (in / mm) | Static Groove Depth | Dynamic Groove Depth | Groove Width (0 Backups) | Groove Width (1 Backup) | Static Squeeze % | Action |
|---|---|---|---|---|---|---|---|---|
| -004 to -050 (0xx) | 1/16" | 0.070" (1.78 mm) | 0.050" – 0.052" | 0.055" – 0.057" | 0.093" – 0.098" | 0.138" – 0.143" | 25.7% | |
| -102 to -178 (1xx) | 3/32" | 0.103" (2.62 mm) | 0.074" – 0.077" | 0.081" – 0.083" | 0.140" – 0.145" | 0.171" – 0.176" | 25.2% | |
| -201 to -284 (2xx) | 1/8" | 0.139" (3.53 mm) | 0.101" – 0.107" | 0.111" – 0.113" | 0.187" – 0.192" | 0.208" – 0.213" | 23.7% | |
| -309 to -395 (3xx) | 3/16" | 0.210" (5.33 mm) | 0.152" – 0.162" | 0.170" – 0.173" | 0.281" – 0.286" | 0.311" – 0.316" | 22.9% | |
| -425 to -475 (4xx) | 1/4" | 0.275" (6.99 mm) | 0.201" – 0.214" | 0.226" – 0.230" | 0.375" – 0.380" | 0.408" – 0.413" | 22.2% |
Why Do Internal-Pressure vs Vacuum Axial Face Seals Dimension Opposite Groove Walls?
When machining a circular axial face seal groove on a CNC vertical mill or lathe faceplate (often surrounded by a bolt pattern from our Machinist Bolt Circle Calculator and Socket Head Counterbore Chart), pressure direction dictates which groove wall prevents seal blowout per NASA Fastener & Mechanical Design Manual (NASA RP-1228) and NIST (National Institute of Standards and Technology) pressure vessel design rules. For Internal Pressure face seals, fluid pushes the O-ring radially outward, so the Outer Diameter (OD) of the groove is sized equal to the O-ring's nominal OD to support the outside of the ring. Conversely, for Vacuum or External Pressure face seals, atmospheric pressure pushes the O-ring radially inward, so the Inner Diameter (ID) of the groove is sized to hug the O-ring ID.
During first-hand shop validation on 6061-T6 aluminum vacuum chambers and 316 stainless hydraulic manifolds, our machinists finish O-ring groove floors to N6 (Ra 0.8 μm / 32 μin for dynamic seals, or Ra 0.4 μm / 16 μin for vacuum face seals) verified with our Surface Finish Ra to Rz Converter, and deburr all lead-in corners with a 15°–20° ramp per our Countersink & Chamfer Chart and NPT Pipe Tap Chart.
| Dash Number | Nominal Size (ID × OD) | Actual ID (in / mm) | Actual CS (in / mm) | Face Groove Depth | Face Groove Width | Internal Press Groove OD |
|---|---|---|---|---|---|---|
| AS568-010 | 1/4" × 3/8" × 1/16" | 0.239" (6.07 mm) | 0.070" (1.78 mm) | 0.052" (1.32 mm) | 0.094" (2.39 mm) | 0.379" (9.63 mm) |
| AS568-014 | 1/2" × 5/8" × 1/16" | 0.489" (12.42 mm) | 0.070" (1.78 mm) | 0.052" (1.32 mm) | 0.094" (2.39 mm) | 0.629" (15.98 mm) |
| AS568-112 | 1/2" × 11/16" × 3/32" | 0.487" (12.37 mm) | 0.103" (2.62 mm) | 0.077" (1.96 mm) | 0.141" (3.58 mm) | 0.693" (17.60 mm) |
| AS568-210 | 3/4" × 1" × 1/8" | 0.734" (18.64 mm) | 0.139" (3.53 mm) | 0.106" (2.69 mm) | 0.188" (4.78 mm) | 1.012" (25.70 mm) |
| AS568-214 | 1" × 1-1/4" × 1/8" | 0.984" (24.99 mm) | 0.139" (3.53 mm) | 0.106" (2.69 mm) | 0.188" (4.78 mm) | 1.262" (32.05 mm) |
| AS568-325 | 1-1/2" × 1-7/8" × 3/16" | 1.475" (37.47 mm) | 0.210" (5.33 mm) | 0.162" (4.11 mm) | 0.281" (7.14 mm) | 1.895" (48.13 mm) |
When machining static face seal O-ring grooves on CNC vertical machining centers, program the groove width so the O-ring locates against the low-pressure wall of the gland. For internal positive pressure vessels and hydraulic manifolds, size the groove outside diameter (OD) equal to the nominal O-ring outside diameter so internal fluid pressure expands the elastomer outward against a solid steel backup wall without stretching the cross-section mid-span.
Conversely, for vacuum chambers and external sub-sea pressure housings, size the groove inside diameter (ID) equal to the nominal O-ring inside diameter so atmospheric pressure pushes the seal inward against the inner steel wall. Never cut sharp 90° internal corners at the top edges of the gland; program a smooth 0.005" to 0.010" (0.15 to 0.25 mm) lead-in chamfer at 15° to 20° so the elastomer slides into the cavity during assembly without shearing.
Frequently Asked Questions About AS568 O-Ring Groove Machining
What corner radius should I use at the bottom of an O-ring groove vs the top edges?
Machine the bottom internal corners of the groove with a generous radius of 0.015" to 0.030" (0.4 to 0.8 mm) to prevent stress concentration, but keep the top entrance edges nearly sharp (0.005" max radius, burr-free) so the O-ring cannot extrude into a wide top corner radius under pressure.
When do I need to widen an O-ring groove for PTFE anti-extrusion backup rings?
Whenever hydraulic system pressures exceed 1,500 psi (10.3 MPa) for dynamic 70-durometer Shore A elastomers—or when diametral clearance gaps are large—add one contoured PTFE backup ring on the low-pressure side (or two backup rings for bidirectional pressure) and widen the groove accordingly.