This is a 743.1 with a grooved base. The grooved base style has only been listed in the most recent guide. It is a feature that is perhaps only of significance to the more detailed threadless collector. The grooved base 743 is a lot harder to find than the more common smooth base versions. The pics should tell the story. I'm looking for 700.00 with the postage. There are 2 other pics of this insulator posted [211789444] & [211789525] Thanks for looking ........ Robin