Just spent 30 minutes scouring the internet for this 'mythical' beast?
Certain posts on MUD by folks claiming to have a socket set including the 'E9' and other posts suggesting alternate methods to remove nuts/studs...but not a single link or source given for the socket. Virtually all the socket sets I could find skip over the E9.
So...does the darn thing exist or not? And if not...why did @IdahoDoug include it in his list of things needed/desired for a HG replacement.
So it appears the overall assessment is right, there is no such animal as an E9. Followed the two provided links or searches, and though the products list a range of these sockets, when the full list of exact included tools is examined, E9 is not included. Neither are many larger sizes.
I have searched for E13 due to my need to open the block plugs for the oil main passage on an International Harvester small V8 engine of 1970's vintage. The plug is an external, square design that is larger than 1/4" and smaller than 5/16" in 8 pt stud socket sizes. Can't double nut due to there being only one to two threads above deck. I started searching for a tool to remove these studs without wrecking them (you can hammer a 1/4" on, but it destroys the stud.) This size tool (9/32"? stud socket) apparently also does not exist. I purchased a 11pc external torx (E-x) set, hoping it would include a tight size adaptation, even if imperfect.) It has several gaps in the provided sizes, seeming to skip odd numbers in the higher range consistently, and, of course, it doesn't include E13, which apparently also does not exist for love or money, and is also the size I need.