Tough insulator to find, with possibly made in Beaver Falls. The guide says M or W, to me it looks like a M. The insulator displays great, but there's a large base chip spanning about 7/16 of the base, the insulator stands up straight still. I added a second picture of the insulator and can send more pictures if needed. The insulator is clean a shiny, doesn't look like it was tumbled or buried. No other issues other than the base chip. Books $500-600, now $200, plus shipping.