Any K-frame threaded barrel should physically screw on, "pinned" or not. The profiles of the barrels are different between light and heavy, and fixed or adjustable sight guns. AFAIK, all of these J&G guns will best match the 2", heavy, fixed sight profiles.

For anything other than a 2", you will also need the longer ejector rod and associated parts.

I finally finished my first one. I'll probably buy a 4" barrel for #2 and shorten it to 3"...