Thread issue - Carlson's Choke Tubes Benelli Nova/SN, Ber Extrema/1301, CZ 712/912, Magazine Extension 10 Shot

I bought this after another extension I recently purchased for my cz712 g2 utility would not thread on the magazine tube no matter what. I assumed it was the wrong part sent so i ordered this particular extension and sure enough same thing! I dont know if the threads are just insanely small tolerances or what but i had to take pliers and force them to thread with all my strength because at this point i was extremely in the hole and frustrated! I couldnt force it all the way down enough for the handguard to be retained so i constructed some makeshift shims. I knew i wasnt cross threading it because i had tried so many times and so may other things, something wierd with my gun i guess but yeah not looking forward to the times im gonna have to remove this bear to try and clean the gun