Explanation dimensions guides.
Very useful basic info which will help you to make the right choice.

For example - guide with dimension 10
- 10 = approx. the inner diameter of the frame so equal to the outer diameter of the ceramic ring insert
- this size dimension is an indication in mm. and can deviate a bit per brand
- for guides without an ceramic insert e.g. hard chrome guides size 10 is equal to the outer diameter of the ring