Just be warey when ordering rings for the 12" DSO Dob OTA. If they are anything like the 10" then the standard rings will be too small. Standard rings for a 10" Newt are 285mm, the outer dimensions of a 10" dob is just over 300mm.
I have the 10" GSO and have been through this exercise. I've replaced the loose nuts that hold the alt bearings on to the tube with captive ones so I can remove/replace the bearings without having to reach inside the OTA. I take the bearings off so the tube can be rotated without the bearing fouling on the dovetail but put them back on for storage or if I can't be bothered setting up the GEM.
I bought rings and dovetail from Star Optics to suit the 10". These were sold separately. I assume you can get rings to suit the 12" also.
Getting rings to suit a 12" is surprisingly difficult. There's nowhere in Australia (that I could find) that manufactures or sells them. So you'll either need to get them custom made, or make them from "bits" like others have done (eg: gas cylinder brackets etc).
I ended up getting mine from Orion Optics in the UK but it wasn't a cheap, timely or a pleasant experience in the end.
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