brass and nickle silver

[Bob C]

Brakie, you are correct as far as appearance of the metal/oxide being covered by paint, but oxides effect the conductivity of the rail (and wheels) in the contact area (top and inner face of the ball or head). Here, the conductivity of the metal and its oxide, the rate of oxidation, and (to a lesser degree) appearance of the rail is important. As for TE, interfaces of like metals - steel/steel, brass/brass, nickel/nickel, are usually relatively sticky. Different metals slip more easily, a characteristic relied upon in making bearings/bushings for rotating machinery, yes ? It's not that brass doesn't do the job, only that (in some ways) nickel-silver is better IMO. Bob