Continuing with Daryl's post...
Four flat staples are clinched into the bottom flat. They are 3/8" long and 5/64" thick. Their feet - that which is set in the barrel metal, are of a diameter that corresponds with a #31 drill bit (can't recall offhand the .000") The rib is inlet for the staples, and a short 1/16" dia. pin secures the wood to the barrel lugs. The rod thimbles are inlet just as you would on a longrifle, and again, secured with a short 1/16" diameter pin. I make my pins of welding rod or nails.
Advantages of wooden rib: adds very little weight to the barrel...requires no soldering skills...cheap to make.
Disadvantages: considerably more fragile that a steel rib, but still quite robust.