Nitrile (Acrylonitrile-Butadine Copolymers) (usually black) – Good physical properties for diving applications, is not considered oxygen compatible.
Viton (Fluorocarbon Elastomers) (usually brown) – Required for oxygen clean applications. There is some controversy because it degrades quickly (including flaking) and is toxic when burned.
Polyurethane (white) – Sometimes used for the face of K-valves, very tough but sensitive to UV light so damaged by exposure to sunlight.
WARNING: material cannot be identified by colour.
Common sizes used in scuba diving
Two dimensions describe the size of an O-ring: its inside diameter and its cross-sectional diameter (CS).
O-rings are described according to AS568B Aerospace Size Standard for O-rings, published by the Society of Automotive Engineers. AS568B lists the sizes of o-rings in six series or groups. The first five series are based on cross-sectional diameter.
O-rings are identified by a 3 digit number: the first digit identifies the series (i.e. the cross-sectional diameter/CS), the second 2 digits are an identifier of the o-ring from the list and not a measurement. O-rings are listed in order of size, so a smaller 2 digit identifier will refer to an o-ring with a smaller inside diameter.
For scuba diving, we use o-rings from the 0XX series (CS 1.78mm | 0.07in), 1XX series (CS 2.62mm | 0.103in), and 2XX series (CS 3.53mm | 0.139in).
||24.99mm | 0.984in
||12.37mm | 0.487in
||10.77mm | 0.424in
||Small DIN regulator
||14.00mm | 0.551in
||12.42mm | 0.489in
||10.82mm | 0.426in
||Large LP port
||9.25mm | 0.364in
||HP port, manifold
||7.65mm | 0.301in
||6.07mm | 0.239in
||Second stage regulator
||1.42mm | 0.056in (CS 1.42mm |