As I recall if installed to "Factory Specs" a Poly had the bbl itself threaded, A Cutts had a threaded adapter Silver Soldered to the bbl & a Herter Vari-Choke had a reduced dia turned a little back of the muzzle. A split threaded ring was then placed in this area & the choke threaded on to it, locking the ring in place. I can't say about any other brands.

Miller/TN
I Didn't Say Everything I Said, Yogi Berra