Practice Tips #100: O-rings 101

American Dental Accessories is proud to present our 100th Practice Tips newsletter! Since 2008, we have been appearing in your inbox with useful maintenance and equipment repair tips to empower your independence and reduce overhead costs. This month, we discuss a common thread throughout all of your dental supply, repair, and maintenance needs: O-Rings 101!

O-rings exist in many types of equipment throughout the dental office. O-rings are in handpieces, delivery system blocks, air/water syringes, and autoclaves — even in the hydraulics of your dental chair. They can serve vital functions sealing various valves or even holding components together.


An o-ring consists of a circular material used to form a circular seal. Not only is the o-ring round, but the cross section of the material is a perfect circle as well. A gasket that has a different shape is not an o-ring. While o-rings can be used as gaskets, not all gaskets are o-rings.

Cross Sections

The circular shape and cross section defines an o-ring. What is a cross section? Simply stated, it’s the shape and thickness of the material. If one were to cut an o-ring and look at the end, the cross section is the shape you’d see (in the case of an o-ring, a circle). Obviously, you don’t need to actually cut the material to determine the shape—simply feeling it will allow you to make such a conclusion. For example, the cross section of your forearm is a rough oval, but you don’t need to cut your arm off to make this determination (NOTE: please don't try this).

O-ring Cross SectionAs o-rings are perfect circles formed from perfect circles, they are also measured in only two dimensions – inside diameter (i.d.) and cross section (c.s.). Mathematically, this makes sense. With the i.d. and c.s., you can easily extrapolate the outside diameter (o.d.). See our Practice Tip #95 for more common dental terms and abbreviations.

However, o-rings are made to exacting tolerances, so it really isn’t practical to measure them. For instance, the standard syringe tip o-ring (#01-04) has an i.d. of 0.114” (+/-.005”) and a c.s. of 0.070”. Taking into account the elasticity, even if you have precise calipers, it’s still extremely difficult to avoid compressing the o-ring when attempting to measure. The best way to measure them is to compare a sample to a sizing chart, we offer a handy o-ring sizing page in our catalog or you may print off the sizing chart by clicking here.

Industry Standards of O-rings

An entire industry dedicates to the manufacturing of o-rings with a variety of standard sizes. An industry numbering system exists just for them. Even more interestingly, many dental manufacturers incorporate the o-ring industry part number into their part numbers.

For example, our #18-OR-002 is the same as the o-ring industry #002 (sometimes referred to as a 1-002). The A-dec part number for this same size is 030-002-02 (or 030.002.02). Note the “002” in the part number; this can help you cross-reference some o-rings very easily.

O-rings are so common they have their own numbering system by the industry. Manufacturers use them in equipment because of the availability . Many of the “standard” o-rings throughout your equipment (and in both our deluxe and standard kits) use the numbered sizes.

O-ring Materials

O-rings are made from a wide range of materials. In view of their role in the dental office, they are usually made out of a flexible material, typically a synthetic rubber. These materials are made in a whole rainbow of colors, so any individual o-ring can exist in any color. Many manufacturers color-code theirs for specific applications, but do not assume its suitability or size based on color alone. As such color-coding provides individualization per manufacturer and ultimately arbitrary.

Just because your original o-ring was green, it does NOT mean you can only replace it with a green one. In fact, a green o-ring might not even be correct. You simply need to find the correct size, regardless of color. The numbering system referenced above can also help in determining the correct one for your application. For simplification, the vast majority of o-rings we stock are black.


While color doesn't matter, its materials ability to withstand the rigors of sterilization is important. It’s important your o-ring can be sterilized if used in a device that needs sterilization. Since they have many different applications, American Dental Accessories only stocks autoclavable o-rings.

No matter what you’re using one of our o-rings for, be assured it’s safe to sterilize if necessary. You don’t need to worry about keeping them separated based on application. Keep them stored by size for all of your equipment in an organized bin. Or purchase a kit with multiple o-ring sizes for any of your needs.

PHOTO: Our deluxe o-ring kit repairs vacuum valves, syringes, and more (item #18-OR-85).

This Practice Tips on o-rings repair 101 hopefully explained all of the information you need to replace them accurately. Like light bulbs, sterilizer door gaskets, and other frequently replaced equipment parts, the added benefit of having common dental o-rings on hand keeps operatories up and running and reduces expensive service calls.


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