[68bird400HO]

Originally Posted by compsur

Thanks for this great info.....In breaking it down and focusing on 80 lbs. units only:

-6462137: First pic, acorn type, was a valid part number until 69

-6460992: Second pic, superseded 6462137, in either gold cad or black finish depending on application. Also found this link on eBay, someone is selling an NOS unit for 700 bucks, a bit more than what I want to spend.
https://www.ebay.com/itm/NOS-1969-74...t/323616162201

-15591103: 3rd Pic, is this the one that is referred to as the INTROL unit?

The third one is NOT the Introl unit. That is just a standard later replacement. The Introl units were more of a dome shape and stamped Introl up by the electrode. I think there are pictures in an old PY thread of one.