I recently purchased a barrel for my Ithaca model 51. It came with 2 Trulock choke tubes. Where do I measure them to determine what I have? I measured 0.7925 on the choke body above the threads. I want to buy some extended chokes for duck hunting.

Tru-Choke reamer that will cut for .795” diameter choke tubes at 44 TPI and a Tru-Choke Thin Wall reamer that cuts .775” at 44 TPI for thin barrels. The Tru-Choke will accept Tru-Choke choke tubes, while the thin wall will only accept the Tru-Choke Thin Wall Tubes.

It sounds like you have a standard Tru-Choke.

I use Trulock Precision Hunter Modified choke with Federal #7 Heavy Weight shells in a 20 gauge for Stuttgart ducks. It will definitely put them down on the water when I do my part! These are my favorite after market choke tubes.