I tried brass at first. Some of you who got early versions or prototypes have brass. Then I switched to stainless. The brass actually had more galling than the stainless. Not sure why. Are you sure the car side with the machined slots is stainless? There's also another difference - my guide pins are a couple thousands larger diameter because it is difficult to find pin stock (any material) in the size used on the Tesla connector. Generally a larger guide pin will have less friction and it feels a little more solid in the car but there is very little difference.