I knew if I waited long enough someone would ask this question, saving me all that time searching for a nut that fit the rod's thread then finding a tap that fit the nut. I bought a box of small billiard balls the size of an 1800 shift knob at an overstock place with the intention of threading the 8 and cue for this purpose. In the 50's and 60's 8 ball knobs were all the rage in hot rods, although the cue ball has a certain dignified elegance. The rest of the balls can be used for practice.