AS568-218 O-Ring

Inside diameter 1.234″
Cross-section 0.139″
Outside diameter 1.512″
Metric (ID × CS) 31.34 × 3.53 mm

OD is derived: ID + 2 × CS = 1.234″ + 2 × 0.139″ = 1.512″.

Neighboring sizes (CS 0.139″ series)

Dash ID OD ID mm vs -218
-216 1.109″ 1.387″ 28.17 ID −0.125″
-217 1.171″ 1.449″ 29.74 ID −0.063″
-218 1.234″ 1.512″ 31.34
-219 1.296″ 1.574″ 32.92 ID +0.062″
-220 1.359″ 1.637″ 34.52 ID +0.125″
Data provenance. SAE AS568, Aerospace Size Standard for O-rings (SAE International). Nominal dimensions per AS568; size tolerances vary by dash number and are not yet cataloged. Groove/gland design depends on the application — consult a gland design reference. See all data sources.