What size is an AS568-371 o-ring?

An AS568-371 o-ring has an inside diameter of 8.4750 in (215.270 mm) and a cross-section of 0.2100 in (5.330 mm), giving an outside diameter of 8.8950 in (225.930 mm).

What is an AS568-371 o-ring in mm?

215.270 mm inside diameter × 5.330 mm cross-section, 225.930 mm outside diameter. AS568 is an inch standard, so these are exact conversions rather than metric nominal sizes.

What is the tolerance on an AS568-371 o-ring?

AS568 allows ± 0.0500 in (± 1.270 mm) on the inside diameter and ± 0.0051 in (± 0.130 mm) on the cross-section, measured free-state.

What groove depth does an AS568-371 o-ring need?

For face seal, static service, a gland depth of 0.1470 to 0.1659 in (3.734 to 4.214 mm), which gives 21–30% squeeze on the 0.2100 in cross-section. Groove width and corner radius come from the seal manufacturer's chart.

Which AS568 series is the AS568-371 o-ring in?

Dash 371 is in the 309-395 band — AS568 3/16 in series, a 0.210 in cross-section. Every size in that band shares the same cross-section and therefore the same gland depth.

AS568 · dash 371 · 0.210 in cross-section

AS568-371 O-Ring Size — ID, Cross-Section, OD and Gland Data

https://shopmath.org/o-rings/as568-371 · data verified August 1, 2026

An AS568-371 o-ring is 8.4750 in (215.270 mm) inside diameter with a 0.2100 in (5.330 mm) cross-section, giving a 8.8950 in (225.930 mm) outside diameter. Static glands for this cross-section run 0.1470–0.1659 in deep. Dimensions are free-state, before installation.

Dash: 371
ID: 8.4750 in
CS: 0.2100 in
OD: 8.8950 in
Series: 309-395

AS568-371 o-ring · inside Ø × cross-section

8.4750 × 0.2100 in

Inside Ø: 215.270mm
Cross-section: 5.330mm
Outside Ø: 225.930mm

Free-state dimensions with AS568 tolerances of ± 0.0500 in on the ID and ± 0.0051 in on the cross-section.

AS568-371 O-Ring Dimensions and Tolerances

An AS568 o-ring is specified by its inside diameter and cross-section; the outside diameter follows from them. Tolerances are the AS568 free-state limits, measured uninstalled.

AS568-371 o-ring — inside diameter, cross-section and outside diameter with tolerances
Dimension	Inch	Millimetre
Inside diameter (ID)	8.4750 ± 0.0500	215.270 ± 1.270
Cross-section (CS / W)	0.2100 ± 0.0051	5.330 ± 0.130
Outside diameter (OD)	8.8950	225.930

OD = ID + 2 × CS. Elastomer parts are measured free-state and relax over time; the tolerances above are manufacturing limits, not the installed dimensions.

AS568-371 O-Ring Size in Millimetres

AS568 is an inch standard. These are the same dimensions converted exactly (1 in = 25.4 mm) — an AS568 size is not interchangeable with an ISO 3601 metric size that happens to be close.

AS568-371 o-ring — metric dimensions
Dimension	Inch	Millimetre
Nominal ID × CS	8.4750 × 0.2100 in	215.270 × 5.330 mm
Nominal OD × CS	8.8950 × 0.2100 in	225.930 × 5.330 mm

Metric figures are conversions of the AS568 inch dimensions, rounded to 0.01 mm as the source data carries them. A metric o-ring called out as 25 × 3.5 mm is a different part.

Static Gland Depth for a AS568-371 O-Ring

Squeeze and gland depth for the 0.210 in cross-section band this size belongs to, from MIL-G-5514G. Depth is what the groove is cut to; squeeze is what the ring gives up to seal.

Static gland squeeze and depth for the 309-395 cross-section series
Property	Squeeze		Gland depth
Application	%	in	in	mm
Face seal, static	21–30	0.0441–0.0630	0.1470–0.1659	3.734–4.214

Static applications only — this reference carries no verified squeeze band for dynamic (reciprocating or rotary) service, so none is shown. Groove width, corner radius, diametral clearance and back-up ring dimensions are outside the verified dataset and must come from the seal manufacturer's design chart.

AS568 O-Ring Sizes Closest to AS568-371

Ordered by how close the inside diameter is, across every cross-section series. A near-ID match in a different cross-section will not seal the same gland.

AS568 o-ring sizes with an inside diameter closest to AS568-371
Property	Inside Ø		Property	Property	Property
Size	in	mm	Cross-section, in	Outside Ø, in	ID difference, mm
AS568-446	8.4750	215.270	0.2750	9.0250	+0.000
AS568-268	8.4840	215.490	0.1390	8.7620	+0.220
AS568-173	8.4870	215.570	0.1030	8.6930	+0.300
AS568-172	8.2370	209.220	0.1030	8.4430	-6.050
AS568-267	8.2340	209.140	0.1390	8.5120	-6.130
AS568-372	8.7250	221.620	0.2100	9.1450	+6.350

Check the cross-section before substituting: the gland depth is set by cross-section, not by inside diameter.

Sources and Method for the AS568-371 O-Ring Size

Size and tolerancescomputed+compiled

bd_warehouse o-ring_parameters.csv (Apache-2.0) and bckasper3/KasperCalc oring-sizes.js (MIT), agreeing on all 349 sizes; OD computed as ID + 2 x CS

Verified against two independent open datasets agreeing on all 349 sizes; fabricated-dataset negative control passed; 21 checks total

Part computed from the standard's formulas, part compiled from agreeing public sources.

Gland designcomputed

MIL-G-5514G (public domain) gland design criteria; squeeze-percentage bands cross-read from Parker O-Ring Handbook ORD-5700 Design Charts 4-2/4-3 (verification only); depth = CS - CS x squeeze%

Verified against computed depth band brackets the published design-chart band for every series

Computed from the standard's formulas, then checked against published tables.

Formula

Outside diameter

OD  =  ID + 2 × CS

  8.4750 + 2 × 0.2100  =  8.8950 in

Gland depth from squeeze

depth  =  CS − (CS × squeeze%)

Squeeze percentage bands are the MIL-G-5514G static criteria; the depth column is that percentage applied to the nominal cross-section.

Assumptions

Dimensions are free-state, at room temperature, before installation.
Tolerances are AS568 manufacturing limits. Compression set, swell in service fluid and thermal expansion all move the installed dimensions and are properties of the compound, not of the size.
Gland figures are for static service only. MIL-G-5514G is inactive for new design and is used here as a public-domain source for the static squeeze bands.
Dataset scope: A fabricated-dataset negative control is asserted against on every run. EXCLUDED: groove width, corner radius, diametral clearance, back-up ring widths, surface finish, all dynamic glands, the 900-series, and ISO 3601 metric sizes.

Data last verified

August 1, 2026

How this data is built and checked →

How to Cite This AS568-371 O-Ring Reference

Citation

ShopMath. "AS568-371 O-Ring Size — ID, Cross-Section, OD and Gland Data." ShopMath, verified August 1, 2026, https://shopmath.org/o-rings/as568-371

BibTeX

@misc{shopmath-o-rings-as568-371,
  title        = {AS568-371 O-Ring Size — ID, Cross-Section, OD and Gland Data},
  author       = {{ShopMath}},
  year         = {2026},
  howpublished = {\url{https://shopmath.org/o-rings/as568-371}},
  note         = {Data verified 2026-08-01}
}

Permanent URL

https://shopmath.org/o-rings/as568-371

Common Questions About the AS568-371 O-Ring

What size is an AS568-371 o-ring?: An AS568-371 o-ring has an inside diameter of 8.4750 in (215.270 mm) and a cross-section of 0.2100 in (5.330 mm), giving an outside diameter of 8.8950 in (225.930 mm).
What is an AS568-371 o-ring in mm?: 215.270 mm inside diameter × 5.330 mm cross-section, 225.930 mm outside diameter. AS568 is an inch standard, so these are exact conversions rather than metric nominal sizes.
What is the tolerance on an AS568-371 o-ring?: AS568 allows ± 0.0500 in (± 1.270 mm) on the inside diameter and ± 0.0051 in (± 0.130 mm) on the cross-section, measured free-state.
What groove depth does an AS568-371 o-ring need?: For face seal, static service, a gland depth of 0.1470 to 0.1659 in (3.734 to 4.214 mm), which gives 21–30% squeeze on the 0.2100 in cross-section. Groove width and corner radius come from the seal manufacturer's chart.
Which AS568 series is the AS568-371 o-ring in?: Dash 371 is in the 309-395 band — AS568 3/16 in series, a 0.210 in cross-section. Every size in that band shares the same cross-section and therefore the same gland depth.

Complete AS568 size chart · Every AS568 series