Sealing Technologies

O-Rings – From Buna O-rings to X-rings

We have one of the world’s most readily available inventories of o-rings and related accessories

Three simple words, but they have a big impact on how your business performs. We know that having the right o-ring at the right time is crucial to your operation because industrial o-rings are our business. Dichtomatik carries more than 10,000 SKUs including the broadest range of top quality industry standard parts, all available with material batch traceability and cure date.
And if you need something custom, our engineering and design team can help assist with your unique o-ring requirements. Our distribution and fulfillment operation is available to assist and improve your ability to deliver on orders, provide the tools to help you sell more products to your customers, and increase your bottom line by ensuring you have the right product in stock.

When you work with Dichtomatik, expect solutions.



From a sealing standpoint, two characteristics make an o-ring.  An o-ring—the shape and the material of construction.

The shape is a circular torus or doughnut-shaped ring (see diagram at right). As can be seen, only two of the three primary dimensions—the inner diameter (ID), the outer diameter (OD) and the cross-section (CS)—are required to completely specify the size of an o-ring.


An o-ring seal has two basic components:

  • The o-ring
  • The enclosed space that both compresses and contains the o-ring

The compression (or more accurately the deformation) of the o-ring provides part of the sealing function. An additional sealing function is realized when the o-ring is activated by the pressure of the gas or liquid that the o-ring serves to contain. The containment ensures that the sealing function is maintained
by keeping the o-ring where it needs to be.



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Click on the image to Download Chart.
Click on the image to Download our complete O-Ring Nomenclature


Dichtomatik offers o-rings in almost any size and in a wide range of materials. We are tooled on most standard o-ring sizes and maintain a large inventory of all AS568 sizes in many different materials.


Most static o-ring seals are one of the three types shown below. In the male gland seal the groove for the o-ring is machined into the piston (the part that is inserted into the bore) and that part with the o-ring installed on it is inserted into the bore. The o-ring seals radially. In the female gland seal the groove for the o-ring is machined into the bore and a smooth rod is inserted through the installed o-ring. As with the male gland seal, the o-ring seals radially. For the face seal, the groove is machined into the face that is perpendicular to the piston or rod. The o-ring seals axially.

The variable names presented in these diagrams are used throughout our design guide.  For detailed information download our O-Ring Handbook.


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 These tables are intended to assist the user in determining the suitability of various elastomers in many different chemical environments. The ratings are based on a combination of published literature, laboratory tests, actual field experience, and informed judgments. As laboratory tests do not necessarily predict end-use performance, users of DICHTOMATIK products should conduct their own evaluations to determine application suitability.

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Many factors other than the gland design, specified o-ring size and elastomer selection can impact the performance of the o-ring in a sealing application. These additional factors have to do with manufacturing, inspecting and storing the o-rings properly and are typically addressed by a good quality assurance program.

Three factors that are of particular importance when dealing with o-rings are:

Manufacturing Quality Systems

The vast majority of o-rings that DICHTOMATIK offers are manufactured in facilities that are ISO-9001 certified. While these quality systems do not guarantee perfect parts, they do typically justify the associated overhead and the resulting increased cost by ensuring that the parts are manufactured, inspected and handled in a consistent manner. Details regarding manufacturing quality systems are available from many other sources and are not specific to o-rings so they will not be presented in this handbook.

Surface Quality

The surface quality of an o-ring has a significant impact on its sealing performance. Several industry standards exist that define surface quality defect types and set maximum acceptable sizes for each defect type. For assistance our Engineers are here to help.

Storage/Shelf Life

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Extrusion or Nibbling

The seal develops ragged edges, generally on the low-pressure side, which appear tattered. This condition is more common with high pressure systems.

Over Compression

The seal exhibits parallel flat surfaces corresponding to the sealing surfaces. May also develop circumferential splits within the flattened surfaces.

Heat Hardening/thermal Degradation

The seal may exhibit radial cracking on the highest temperature surfaces, often accompanied by the flattening of the seal characteristic of over-compression. Certain elastomers may exhibit signs of softening, such as a shiny surface.

Spiral Failure

The seal surface exhibits a series of deep, spiral, 45°-angle cuts. This failure is often seen with long-stroke, hydraulic piston seals.

Chemical Degradation

The seal may exhibit many signs of degradation including blisters, cracks, voids or discoloration. However, in some cases the degradation is only detectable by measurement of physical properties.

Explosive Decompression

Explosive decompression results when high-pressure gases are absorbed by the seal, and then, as the pressure is rapidly dropped, the expanding gasses are trapped in the micropores of the elastomer, causing surface blisters and ruptures as they escape.

The effected seals will exhibit random short splits or ruptures deep into the seal cross-section. When first removed the surface may also be covered with small blisters.


Abrasion occurs only with dynamic seals—seals involved with a rotary, oscillating or reciprocating motion. The seal or parts of the seal exhibit a single flat surface parallel to the direction of motion. Loose particles and scrapes may be found on the seal surface.

Plasticizer Extraction

Seen primarily in fuel systems, plasticizer extraction is characterized by a loss of volume or weight of the seal. It is often difficult to detect with only a visual inspection.

Installation Damage

The seal or parts of the seal may exhibit small cuts, nicks or gashes.

Weather Or Ozone Cracking

Occurring in seals exposed to ozone, UV radiation or other air pollutants, weather or ozone cracking is characterized by small surface cracks perpendicular to the direction of stress.