I know that there was an old, interesting thread about the finish on disc brake proportioning valves. Here is what I found on one example:
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The original paint on the back side is definitely black. After painting, certain areas were machined and left bare. The threaded part appears to be clear zinc or cadmium plating. The adjuster nut is the same or zinc dichromate (yellow/gold)-I cannot determine that until it is disassembled.
This particular valve appears to be original to the car with a date of "120-5" which translates to the 120th day of 1965 (April 30, 1965.) This is a very late '65 San Jose production car built around the end of June or the beginning of July. Just thought that some here would find this interesting.
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