I don’t completely understand what you exactly mean about metric tenon threads on the barrel, but mine still showed a little bit of threads after I screwed on the area 419 hellfire muzzle brake. I checked with sig and area 419 and the problem is more cosmetic than anything. Apparently if you purchase a sig muzzle brake it will hide that last thread or so. I don’t even notice it anymore. FYI, the hellfire brake is phenomenal!