Browing Sweet 16

Recently picked up a 1951 Browning Sweet 16. It has a 22 inch vented rib barrel. I believe it may have had a poly choke cut off of the barrel, and a screw in choke added. Now my question. the only markings on the choke tube are TC with the word MOD under that. I assume the MOD is modified but anyone know if the TC is for Tru-choke? or Tompson Contender? Or is there another Mfg? Would like to order maybe an improved and a full, but not sure what thread or size to order Thanks