These rings are designed for models of mine. 
(There are some exceptions, such as my collector and hole model.)

I've made some minor adjustments to the ring's dimensions, but updating all rings from older models is a big job. So, I'm thinking of uploading these ring as individual models.

There is no difference in performance. It's just a slight adjustment in dimensions.
Due to the variability in print environments, I offer 5 different fit options. 

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25/1/28 added 14.825mm and 14.875mm version.

Note : If you need a tighter or looser fit, please let me know.