I've had the glass insulator for a while, but the wonderful letterhead from The Electrical Supply Co of Chicago was an item that I was able to purchase at the recent NIA Convention in Boxborough, MA. The letter is dated July 25, 1891. Very cool go-with. I've posted some other letterheads around this site, including this one: [id=247415115] I should have photographed to back too, as it has a wonderful incandescent light illustration.