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Technical Information

Seal & Design is a world-class seal & gasket manufacturer and a name you can trust for gasket, seal and o-ring solutions.  Technical sealing has been defined by DIN Standards as follows:

• Static Seal – The sealing action created between two mating surfaces with no leakage of liquid or minimal diffusion of gas.
• Dynamic Seal – The mating surfaces have relative movement with minimal leakage of liquid (useful to protect the sealing efficiency, acting as lubricant)

The simple geometry is the main characteristic of an O-Ring which, in conjunction with proper elastomer selection results in a low cost, easy to use and efficient sealing system. Elastomeric materials, when compressed, react like a high viscosity fluid which transmits applied stress in every direction; consequently, the O-Ring serves as a barrier, blocking the leak paths between the sealing surfaces.

O-Rings offer several advantages over other sealing systems: simplicity of construction, standardized seal dimensions, wide selection of materials, suitability for both static and dynamic applications, standard dimensioning of glands, low cost due to high volume manufacturing.

Sealing is always achieved through a positive compression or squeezing action, resulting in a deformation of the O-Ring cross-section. The most important sealing characteristic of an O-Ring is its resistance to compression set or residual deformation.

O-Ring Sizes: Standard & Metric Sizes

There are two main o-ring sizing types: standard and metric. Standard was developed for use in the United States, while the international community uses metric sizes. The metric sizes are further broken down by region, notably Europe and Japan.

Learn more about O-Ring sizes with the links below.

Seal & Design has all these sizes and more. We can provide virtually any required size.

Standard Size O-Rings (AS568B)

The standard sizes used by o-ring manufacturers in the United States are defined by Aerospace Standard AS568B, Aerospace Size Standard for O-rings. That document, published by the Society of Automotive Engineers (SAE), lists the sizes of O-rings in six series or groups in both inches and millimeters. The first five series are based on cross-sectional diameter. The sixth series includes 20 sizes for boss seals. The standard sizes are also used for most military specifications.

Cross-sectional diameters range from 0.040 to 0.275 inch. Inside diameters range from 0.029 to 25.940 inches. There are 369 standard sizes.

Metric Size O-Rings

Standard metric sizes for O-rings are defined by International Standard ISO 3601-1:2002: Fluid power systems O-rings Part 1: Inside diameters, cross-sections, tolerances and size identification code. That standard groups metric sizes into two series, G and A. The G series is used for general purpose applications and includes a wide range of inside diameters. The A series is used for aerospace applications where tighter tolerances are recommended. The G series has 445 sizes and the the A series has 383 sizes.

Currently, ISO sizes do not use a dash numbering system like the Aerospace Standard. ISO cross-sectional diameters differ from the Aerospace Standard by less than 0.001 inch. Therefore, many AS568B sizes are interchangeable with an ISO size. Be sure to consult ISO 3601-1 for specific dimensions, as inside diameters may differ.

Standard Size O-Rings (AS568B)

We stock a full line of o-rings in a wide variety of sizes, shapes, and compounds. Popular offerings include: Viton® O-Rings, Buna-N O-Rings, Silicone O-Rings, Chemraz® O-Rings, EPDM O-Rings, PTFE O-Rings, Neoprene O-Rings, Metric O-Rings, Back-Up RingsX-Rings, Square Rings, Spliced O-Rings. We also make custom o-rings for specific applications.

O-Ring Offerings


O-Ring Special Features Available

  • Special packaging, barcoding, and private labelling
  • Silicone coating
  • Dipped external o-ring lube designed for ease of installation
  • Moly/Graphite Lube
  • Molybdenum dasulfide external o-ring lube
  • Parafin filled – internal
  • Wax based o-ring lube – moderate lubridity
  • Silicone lube – internal
  • O-rings or special molded parts can be produced in any color