O-rings

Parco is your convenient source for quality O-rings. We make all 369 standard sizes, hundreds of special sizes, and O-ring kits. We also manufacture standard and custom metric sizes. Parco offers O-rings that meet virtually every military and industrial specification. With more than 100 million O-rings in stock, Parco maintains one of the largest inventories in North America.



Background
An O-ring is a solid-rubber seal shaped like a doughnut or torus. When compressed between mating surfaces, an O-ring blocks the passage of liquids or gases. Two dimensions describe the size of an O-ring: its inside diameter (ID) and its cross-sectional diameter (CS).





Standard O-ring Sizes

There are 369 standard sizes of O-rings with inside diameters ranging from 0.029 to 25.940 inches and cross sections ranging from 0.040 to 0.275 inch. Standard sizes are available in five popular cross-sectional diameters (0.070, 0.103, 0.139, 0.210 and 0.275 inch). Each O-ring size is identified by a "dash number." Each Parco "dash number" is the same as Aerospace Standard AS568B, Aerospace Size Standard for O-rings. Those designations are used throughout the O-ring industry. Parco offers O-rings in all 369 standard sizes and has hundreds of molds for non-standard sizes. In addition, Parco also offers all 20 sizes of boss seals used for sealing straight-thread tube fittings on a boss.

International O-ring Sizes

Standard O-ring sizes are defined by International Standard ISO 3601-1:2008: Fluid power systems—O-rings—Part 1: Inside diameters, cross-sections, tolerances and size identification code. That standard groups sizes into three classes:  Class A for general industrial and aerospace applications, Class B for general industrial applications and an unlettered class for Aerospace Metric Applications. Classes A and B have three-digit Size Codes that are equivalent to the three-digit dash numbers in AS568B.  There are only two differences among AS568B, Class A and Class B:  Classes A and B do not address the 25 sizes of O-rings listed in AS568B as straight thread tube fitting boss gaskets, and Class B offers wider inside diameter tolerances, especially on larger sizes. ISO 3601-1:2008 also lists 360 sizes based on the former Series G Metric Aerospace sizes that were listed in the previous revision of the standard.  The former Series A sizes have been discontinued.  Metric cross sectional diameters differ from AS568B by less than 0.001”.  Therefore, many AS568B sizes are interchangeable with a metric size.  Be sure to consult ISO 3601-1:2008 for specific metric dimensions, as inside diameters may differ.

If Parco does not have a mold for a non-standard size or a particular metric size, we can make one for you.

Below is a list of our Popular Compounds for O-rings. If you need additional help, use Parco’s Compound Wizard to search our compound library.