I have the ASI533MC-Pro, and there is everything in the box to provide 55mm back-focus to an m48 male fitting (which is what my skywatcher coma Corrector has ✅)
However my Altair Astro Lightwave flattener has a T2 male thread 😔 (with the same 55mm backfocus requirement) which meant that I had to find some way of replacing the 16.5mm T2-m48 adapter with something that did T2-T2.
I had no joy finding 16.5, or even 16mm (I could have made up 0.5mm with ZWO-supplied spacer rings). I could have bought two packs of extension rings to provide 2 x 8mm T2 extensions but that was getting costly/wasteful.
I ended up buying a Baader Varilock 46 to replace both the 16.5mm and 21mm ZWO extension tubes, with the advantage that it lets me fine-tune the spacing if needed. This only arrived yesterday so there hasn't been the chance to try it in anger, but I have successfully done a dry fit.
HTH
Ady