O-Rings

High-performance sealing for oil and gas operations.

O-ring diagram marking inside diameter (ID), outside diameter (OD), and cross section (CS)

FIGURE 1 — O-RING CROSS-SECTION AND KEY DIMENSIONS

GENERAL

The Moss Seal O-Ring is a molded, torus-shaped ring of elastomeric material used to create a static or dynamic seal at the interface of two mating surfaces. When compressed in a gland, the O-Ring’s cross-section deforms slightly to fill the groove and block the passage of gas or fluid, making it one of the simplest and most reliable sealing devices in fluid power and general industrial design.

INTERACTIVE MODEL

Explore O-Ring geometry

Adjust standard dimensions, compare materials, and inspect the relationship between inside diameter, cross section, and outside diameter.

O-Ring
Drag to rotate. Change the dimensions and watch the cord change.
Material
Inside diameter50.0 mm
Cross section, AS568 standard widths (mm)
ID50.00
CS5.33
OD60.66
OD = ID + 2 × CS, in mm
Double-click to reset the view

GEOMETRY

Key dimensions

Every O-Ring is defined by three dimensions. Together, they determine the ring’s installed fit, available sealing material, and compatibility with the gland.

ID

Inside diameter

The diameter measured across the inner opening of the ring before installation or compression.

OD

Outside diameter

The diameter across the outermost edge of the ring. OD equals ID plus twice the cross section.

CS

Cross section

The diameter of the molded cord—the material thickness available to fill the gland and seal against system pressure.

OD = ID + 2 × CS

OD = ID + 2 × CS

SPECIFICATION

Materials & sizing standards

6 materials · scroll or use the arrows
NBR

Nitrile

General-purpose with good resistance to petroleum oils and fuels.

HNBR

HNBR

Nitrile with added heat and oil resistance for hot hydraulic oil, sour gas and high-pressure service beyond standard NBR.

EPDM

EPDM

Excellent resistance to water, steam, and weathering; avoid use with petroleum oils.

FKM

Fluorocarbon

High-temperature performance and broad chemical resistance.

FKM

evolast® FFKM

Perfluoroelastomer for extreme heat and aggressive chemicals beyond FKM’s range.

PTFE

PTFE

Chemically inert and suited to applications where elastomers are incompatible with the media.

6 materials · scroll or use the arrows
NBR

Nitrile

General-purpose with good resistance to petroleum oils and fuels.

HNBR

HNBR

Nitrile with added heat and oil resistance for hot hydraulic oil, sour gas and high-pressure service beyond standard NBR.

EPDM

EPDM

Excellent resistance to water, steam, and weathering; avoid use with petroleum oils.

FKM

Fluorocarbon

High-temperature performance and broad chemical resistance.

FKM

evolast® FFKM

Perfluoroelastomer for extreme heat and aggressive chemicals beyond FKM’s range.

PTFE

PTFE

Chemically inert and suited to applications where elastomers are incompatible with the media.

Sizing standards

Moss Seal O-Rings are available in standard AS568 inch and metric/ISO 3601 size series, as well as custom dimensions to match existing gland designs. Standard durometer hardness ranges from 50 to 90 Shore A depending on material and application.

ENGINEERING

Gland design & squeeze

Proper compression

Proper sealing depends on squeeze—the percentage by which the O-Ring’s cross section is compressed when installed in its gland. Typical static applications use 15–30% squeeze, while dynamic applications generally use 10–20% to reduce friction and wear. Too little squeeze risks leakage; too much accelerates compression set and shortens service life.

Advantages

• Simple & compact design

• Low cost per seal

• Wide material selection

• Static and dynamic use

• Easily replaced

• Broad size availability

Parker Distributor
MCM, an Angst+Pfister company, high-performance sealing distributor