How is the size and diameter of O-rings graded?

Dimensioning of O-rings: Only the inner diameter and wire diameter are marked. According to the standard, the wire diameter is: 1.8, 2.65, 3.55, 5.3, 7 (because the standard is made in imperial units, so the metric units are replaced with decimals)

There are many inner diameter specifications, usually relying on the standard.

In actual use, the inner diameter of the O-ring has little effect, and can be selected according to the standard size and assembly relationship. For example, the inner diameter of the O-ring installed on the shaft shoulder can be smaller, and the assembly is tightened on the shaft and is not easy to slip out. The inner diameter of the O-ring installed in the hole can be appropriately larger, and it is easy to rise on the outer diameter during assembly, and it is not easy to be squeezed.

The groove size of the O-ring is the most critical. It is necessary to ensure that the O-ring has sufficient pre-compression and space for expansion and contraction in another direction.