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O-ring Size Chart
and Material Information
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As always these are guidelines and you specific application may take testing and analysis.

O-ring Size Chart and Compound information pages.

 

O-rings – Basic Definition:

O-rings are one of the most common and important parts in almost every moving machine or part. O-rings are available in a large number of standard sizes and material. We will attempt to help you identify the size, compound, and were to purchase the o-rings you needed for all your application.

An O-ring is a loop of elastomer with a round (o-shaped) cross-section used as a mechanical seal. They are designed to be seated in a groove and compressed during assembly between two or more parts, creating a seal at the interface. The joint may be static, or have relative motion between parts and o-ring (rotating pump shafts and hydraulic cylinders, for example). Joints with motion usually require lubrication of the o-ring to reduce wear. This is often accomplished with the fluid being sealed.

O-rings are one of the most popular seals used in machine design because they are inexpensive and easy to make, reliable, and have simple mounting requirements. They can seal many thousands of psi.
Successful o-ring joint design requires a rigid mechanical mounting that applies a predictable deformation to the o-ring. This introduces a calculated mechanical stress at the o-ring contacting surfaces. As long as the pressure of the fluid being contained doesn't exceed the contact stress of the o-ring, leaking cannot occur.

O-ring - History

The US patent claim for the O-ring was filed in 1937 by a then 72-year-old Danish-born machinist, Niels Christensen. He came to USA in 1891 and soon after that patented an air brake system for streetcars (trams). Despite his legal efforts, his intellectual property rights were passed from company to company until they ended up at Westinghouse. During World War II, the US government commandeered the O-ring patent as a critical war-related item and gave the right to manufacture to other organizations. Christensen got a lump sum payment of $75,000 for his efforts. Litigation resulted in a $100,000 payment to his heirs in 1971, 19 years after his death.

AS568A Dash Number O-Ring Sizing

O-ring size is designated by a three digit dash number in the form -xxx. Two dimensions define the size of an O-ring: its inside diameter (ID), and its cross-sectional diameter (CS). Aerospace Standard AS568A , Aerospace Size Standard for O-rings, published by SAE, groups most standard sizes under one of five cross-sectional diameters (or series), as follows:

-000 Series O-rings 0.070" ±0.003" - 1/16" CS
-100 Series O-rings 0.103" ±0.003" - 3/32" CS
-200 Series O-rings 0.139" ±0.004" - 1/8" CS
-300 Series O-rings 0.210" ±0.005" - 3/16" CS
-400 Series O-rings 0.275" ±0.006" - 1/4" CS

 

O-rings – Basic Material:

O-ring selection is based on chemical compatibility, application temperature, sealing pressure, and cost.

Typical o-ring materials:

  • Nitrile (NBR or Buna N)
  • Silicone (VMQ)
  • Fluorocarbon (Viton®, FKM)
  • Kalrez® (FFKM)
  • Fluorosilicone (FVMQ)
  • Ethylene Propylene (EPM, EPDM, EP, EPR)
  • Neoprene (CR, Chloroprene)
  • Polyurethane (AU, EU)
  
   
   
     
     
 Material Selection and size charts for o-rings.