O-Rings

Sources: MIL-G-5514F, Gland Design; Packings, Hydraulic, General Requirements For (1969), Table I and Figure 3, and its 1993 revision G; ring sizes MS28775, the same as SAE AS568. GOST 9833-73, Rubber O-rings for hydraulic and pneumatic equipment (amendments 1 to 3): ring sizes and the recommended seats.

Gland depth: (bore − groove diameter) ⁄ 2 for a groove on a shaft, (groove diameter − shaft) ⁄ 2 for a groove in a bore.

Squeeze, stretch and fill: squeeze = (section − gland depth) ÷ section; the inch figures stack every tolerance in the table. Stretch = (groove diameter − ring ID) ÷ ring ID, for a ring on a shaft. Groove fill = the ring's section area ÷ the groove's area (depth × width).

Face seals (inch): depth = the Table I gland depth; groove OD = the ring's nominal OD for pressure from inside, groove ID = its nominal ID for vacuum; width = the Table I width for no backup ring. Nominal sizes are the dash series' fractional sizes (−007 and −009 in 32nds); −001 to −005 have no face groove here.

Sizes: −013 to −028, −117 to −149 and −223 to −247 are for static seals only (MIL-G-5514G 3.5.3); −020 to −028 and −131 to −149 are not preferred. Metric rings are named shaft – bore – section × 10 (030-035-30: 30 mm shaft, 35 mm bore, 3.0 mm section); only the standard's recommended sizes are listed.

Metric limits: GOST 9833-73 gives the seat sizes as nominal values and the tolerances in its appendix. Table 1 sets the fit of the bore and the shaft by working pressure (up to 5 MPa, over 5 to 10 MPa, over 10 MPa) and by moving or static seal; Table 1a sets the groove: diameter H9 in a bore, h9 on a shaft, width H13, face groove OD H11 and ID h13. Each class is turned into limits with ISO 286. The bore and shaft show the limits across all three pressure bands, with a row for each band; a diameter you type is checked against each band's limits.

Starting from a diameter: the inch and metric series are both searched, whatever the unit switch says. A diameter inside a standard size is an exact match, and that size is shown alone, with every O-ring that fits it (both series when both have one). Otherwise the nearest standard size under the diameter and the nearest over it are shown, whichever series each comes from. Any other O-ring can be chosen from the full list underneath; if the diameter isn't one of its standard sizes, the result says so. Every size reads in the unit you choose, converted where the ring's standard uses the other one.