Standard AS568/Metric O-Rings and Other Sealing Solutions


What is an O-Ring?

An O-Ring, also known as a packing, or a toric joint, is a mechanical gasket in the shape of a torus; it is a loop of elastomer with a round cross-section, designed to be seated in a groove and compressed during assembly between two or more parts, creating a seal at the interface. The O-Ring may be used in static applications or in dynamic applications where there is relative motion between the parts and the O-Ring. Dynamic examples include rotating pump shafts and hydraulic cylinder pistons. O-Rings are one of the most common seals used in machine design because they are inexpensive, easy to make, reliable, and have simple mounting requirements. They can seal tens of megapascals (thousands of psi) of pressure.

O-Rings perform their sealing action by deforming to take the shape of their cavity, after being oversized to guarantee a predetermined interference fit.The seal is designed to have a point contact between the O-Ring and sealing faces. This allows a high local stress, able to contain high pressure, without exceeding the yield stress of the O-Ring body. The flexible nature of O-Ring materials accommodates imperfections in the mounting parts. They can withstand fluid pressures upto 100 bar (1500lbs/in2) provided such seals are properly designed and applied. The pressure ratings of the dynamic O-Ring seal can be enhanced by using suitable back-up rings. The back-up rings may be of acetal resin, PTFE or Fabric reinforced rubber.

Advantages of O-Rings:

  • They seal over a wide range of pressure, temperature and tolerance
  • Ease of service, no smearing or retightening
  • No critical torque on tightening, therefore unlikely to cause structural damage
  • O-Rings normally require very little room and are light in weight
  • In many cases an O-Ring can be reused, an advantage over non-elastic flat seals and crush-type gaskets
  • The duration of life in the correct application corresponds to the normal ageing period of the O-ring material
  • O-Ring failure is normally gradual and easily identified
  • Where differing amounts of compression effect the seal function (as with flat gaskets), an O-Ring is not effected because metal to metal contact is generally allowed for
  • They are cost-effective
  • The Four Main Elements that Define an O-Ring are:

    • Size: O-Rings are available in various metric and inch standard sizes. Sizes are specified by the inside diameter (I.D.) and the cross section (C/S) diameter, or thickness. If the size you need is not a standard AS568 or Metric size, you will need either a Vulcanized O-Ring, or a Custom Molded O-Ring
    • Material: Selecting an O-Ring material for a specific application depends on many important criteria including what is being sealed, temperature range, pressure, dynamic or static, desired service life, installation considerations, tolerances, etc. See our Material Selection Guide for more information on this topic
    • Durometer: The hardness of rubber compounds is measured by the Shore A durometer; the higher the durometer, the harder the compound
    • Color: While there are standard colors that we stock for certain materials/Durometer, you can get any O-Ring in any color
    • An O-Ring is specified by its inner diameter, cross-section diameter, material hardness/durometer (typically defined by the Shore A hardness), and material composition. SourceSync holds stock of most commercially available O-Rings in both Metric and Imperial sizes, available in the following materials: - Nitrile Butadiene, Silicone, Poly Tetra Fluro Ethylene (PTFE), Neoprene, Viton® (Flurocarbon), Polyurethane, Ethylene Propelene Diene Monomer (EPDM) etc. In addition to standard imperial and metric sizes, SourceSync also carries a wide variety of non-standard sizes. With knowledgeable sales people, fast response to quotes, low order minimums, on-time shipments and trustworthy blind-shipping, SourceSync is equipped to help you meet your customer's sealing requirements. We welcome the opportunity to earn your business!

      Click here to view AS568 Standard O-Rings Sizes

      Click here to view Standard Metric O-Ring Sizes

      Click here to view All Standard and Non-Standard O-Ring Sizes


Need help choosing an O-Ring? For assistance with o-ring size or material selection, contact us today.info@srcsync.com(224)-650-7962

O-Rings By Material

SourceSync offers an unrivalled range of over 300 high performance seal materials from the types of elastomer (rubber) shown below. Our Materials Technologists are constantly developing new seal materials to meet the increasing demands of today's engineering applications. We have relationships with major compounders and can provide genuine base polymers from brand name companies.

  • Viton® / FKM
  • Nitrile / NBR
  • Ethylene Propylene / EPDM
  • Fluorosilicone / FVMQ
  • Silicone / VMQ
  • Neoprene / CR
  • Kalrez® / FFKM

O-Rings By Application

An in-depth knowledge of materials, advanced production capabilities and quality assurance methods combined with the zero-defect philosophy allows SourceSync to meet these ever increasing requirements for pressure, temperature, geometry, chemical resistance, hardness and physical stress. A wide range of elastomeric materials combined with specifically engineered coatings are used to transform this “simple” sealing element into a critical component for a surprisingly vast array of applications in all areas of industry.

  • General Appplications
  • FDA Compliance
  • NSF 61 and Water
  • UL Recognized Compounds
  • Oil and Gas

Other Sealing Solutions

SourceSync elastomer materials can be molded into infinite geometries, profiles and sizes to suit any sealing application. From the smallest O-ring to more complex composite parts, our objective is to meet customer needs with a variety of high performance sealing solutions. If the seal you require does not already exist, we can design and manufacture it for you, with the benefit of more than 30 years experience in the sealing industry to draw upon.

  • Backup Rings
  • X-Rings & D-Rings
  • Boss Seals
  • T-Seals, L Seals and Cap Seals
  • Block Vee & U Cups
  • O-Ring Cord