The reason for the finger joints is that all the oak you see on my bench came from an old day bed that I bought for forty dollars. At one time someone spent a lot of money on it, it was all solid oak, and a lot of the pieces were over an inch thick. The chop is made from part of the arms on the bed. The finger joints held them together. The inside piece is from the other end, but turned upside down.
When I first put it together, I just used the two screws. It worked, but it didn't track very straight, and would bind up when you cranked it in and out. I took it apart, and did it right. I added two one inch dowel rods running through bronze bushings. It slid in and out freely with out the nut on it.
On the first version, I tried to just capture the coupling nut on the back side between a couple of pieces of angle iron. That didn't work worth a damn. This time I morticed the hex about half way into the back. When I put it together, I planned to block the nut in solid, and drill it for roll pins so it didn't move in and out. I pushed it shut with my knee, reached down and adjusted the bottom nut, spun the coupler nut up snug, wiggled the crank a little 'til the hex lined up, and spun it tight. Hey wait a minut, why do I want to pin that nut in place again? So I can crank it in and out eight or ten inches when I adjust it? Now I can loosen it three or four turns to disengage the nut, spin the nut out of the way, pull it straight open, lay whatever in it, push it shut, and lock it down. It's much easier than turning that crank 40 or 80 rounds. I even took that knee busting crank handle off of it today. By the way, here's another attachment I made for the back side of my bench.