I bought two ST Sub/GMT bezels recently. They come with your (limited) choice of insert as an online order. You may be able to get any other insert they sell by special request as they are all the same price. I didn't ask because I didn't really need any particular insert. The ST inserts I got were press fit but not gen outside diameter.
The two ST bezels I bought were IMO inferior quality and do not fit a gen insert. I spent a lot of time sanding down the inner perimeter of the bezel rim so I wouldn't have to shave my gen insert and then I decided to re-use a four year old WSO bezel which is more gen-like and took a gen insert straight away. This is not a WSO bezel recommendation as batches change and mine were from so long ago.
There are some pics and more discussion in the link below
Post #150
I might also suggest pressing it on without the click spring. This way you can see if your bezel and retaining ring from two different suppliers are compatible. If it still won’t turn, try without the washer. If it works, then try with the spring. This is good advice. @Michaelarena89 If your...
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