The surplus motors I picked up uses 0.125" square hole. So I ordered the Vex 0.125" 12" shafts and matching collars. These shafts and collars cost as much as the motors!
Anyhow, I'm trying the dual 4" transwheels from kornylak.com, FXA159. These wheels have 1/2" inner hole to mount the wheels. I really appreciate your kind guidence to point me to where I can get some kind of coupler to go from the 0.125" to 1/2" diameter hole, how to mount these together and how to lock the wheel with the 1/2" shaft.
I can cut the 12" smaller shafts down to length so I will keep these as short as possible. I will use 2 of the transwheels for diff. steering.