It says triple threaded, and it looks like there should be threads on the exposed wood of the shaft, but I don't see any. I doubt that the wood/metal contact would do much good anyway.
For the two sets of threads on the pin, I imagine it would not be hard to get the spacing correct, but I think it's pointless. I've heard that for a standard screw connection, three threads basically do all the work. The force is not distributed along the full length of the screw because the metal stretches enough where the the threads are working that the far threads are slack. Or so the theory goes. Any mechanical engineers/machinists here?