Steel adapter accepts Win-Choke style choke tubes. Install by turning the last 3/4" of barrel to the dimension listed and then solder the adapter in place. Gunsmith installation will be required. Alloy steel, 2 1/2" long, .867" outside diameter, accepts Win-Choke tubes.
Dimension in description is the inside diameter of the adapter.
Turn the final 3/4" of the outside of the barrel to the description dimension, then solder the adapter in place.