Thompson Center Contender .410 Shotgun (21") Barrel Chokes

[Sidewinder]

I need some expert information on the choke tube system installed in Thompson Center 21" .410 Shotgun Barrels. This is not the 45 Colt/.410 pistol barrel. This is a TC manufactured barrel and it has one "Full Choke" choke tube installed in it. I presume it was installed at the factory. I have been looking for a "Modified" and a "Improved Cylinder or Cylinder" choke tubes for it. I've contacted some and no one seems to know the details on the choke tubes for this little shotgun barrel. Now, this "is not" an Encore barrel, it's a Contender barrel. I'm not sure if they ever made a .410 barrel for the Encore. I've only heard of 12 & 20 gauge. I need to know if TC put out a choke tube "system" for this .410 Contender barrel. If there was only one choke tube..."Full Choke"... why bother, just build the barrel as a Full Choke barrel. I ordered a set of Beretta choke tubes from Brownell's, but they would not fit. The threads on the Full Choke tube that came with the barrel, has the threads up near the muzzle, and the threads are courser than most choke tubes. Educate me please!

[Sidewinder]

With the vast pool of firearms knowledge on this site, I was certain someone could tell me what choke tube system the TC Contender .410  21" vent ribbed shotgun barrel used. The threads are right up by the muzzle and they are coarser than my Rem-Choke threads. Any help is greatly appreciated.