Here are some mechanical and eldectrical starter solenoids.I think one of those mechanical/foot-starter solenoids has the side-post which HotRodLincoln refers to - it was not needed on 6v vehicles.
Nonetheless, I think that both types of mechanical-solenoids can be used with 6v or 12v starters/systems.
I did not check part numbers to see if that 1954 6v electrical-solenoid could be used on a 12v system. I think it could be used on 6v (positive/negative ground) 1952-1955st GMC/Chevrolet trucks with Hydra-Matic transmissions.
