Because of its popularity there is virtually an unlimited number of possible sizes of an o-ring. All 25karats rings are manufactured in US standard ring size. TIPS FOR BUYING THE RING AS A SURPRISE Ask.
An o-ring is one of the most common types of seals in the world.
In the US ring sizing system an average lady has a finger size of approximately 65. In Italy Spain Netherlands and Switzerland ring sizes are specified as the circumference minus 40mm. Thus the need for size standards which cover the most common sizes used. Ring Size Conversion Chart International Ring Sizes.