Gunsmithing Minimum muzzle diameter for QD Can mount?

Typically you see .100" of barrel wall minimum recommended. You can do 7s and 30 Cal's at 1/2-28 but it's not ideal. Much more likely to impact accuracy.
 
A lot of times people will go 9/16-24 on thin barrels then silver solder on an adapter to step up to 5/8-24. Maximize wall thickness and get you up to a common thread pitch for the caliber.
 
This adapter can take 9/16-24 up to 5/8-24:


I’m currently sitting on one, but haven’t used it yet. FWIW I’ve had nothing but good experiences with Precision Armaments.