We usually show an o ring as ID*CS, ID is short for inner diameter, CS is short for cross section. Somebody also show an o ring as OD*CS, OD is short for outer diameter, CS is short for cross section.

So there is a formula for o ring. OD=ID+2*CS, or ID=OD-2*CS.

You can know what is an o ring from the picture as bellow:

We supply different standard o rings with different materials, of course can be in different colors.

AS568 Standard usually share the same CS (cross section), the value of CS usually is 1.78mm, 2.62mm, 3.53mm, 5.33mm or 6.99mm. But ID (inner diameter) are very different, from 0.74 mm to 658.88 mm.

JIS B 2401 Standard usually share the CS as 1.90mm, 2.40mm, 3.10mm, 3.50mm, 5.70mm, 8.40mm and so on.

Besides, we also supply non-standard o rings, CS from 0.5mm to 30mm, ID from 0.5mm to 2000mm.

And about matrial, we have NBR, FKM, SILICONE, EPDM, CR, AEM, NR, HNBR, PU and so forth.

NBR is the abbreviation for nitrile butadiene rubber, also known as nitrile rubber, the basic advantages as bellow:

1. Good oil resistance: It has excellent resistance to oils and lubricants, making it suitable for applications in environments with oil contact.
2. Abrasion resistance: It shows good resistance to wear and abrasion.
3. Low temperature flexibility: Can maintain certain flexibility and elasticity at relatively low temperatures.
4. Good sealing performance: Useful in sealing applications to prevent leakage.

For example, NBR is often used in seals for automotive and industrial equipment where it needs to resist oil and provide a good seal. It can also be found in hoses and gaskets that operate in oily  challenging environments.

But NBR is poor performance when exposed to UV, general weathering and ozone. It is therefore not advisable for outdoor applications.