I had a Jeunet 10-speed in the mid 70s. Very nice light weight bike. Rode it across Iowa on RAGBRAI 5. Was not a big fan of the pins that held the pedal arms on the shaft.
Years ago I was changing plugs on my 75 Buick. Dropped the socket, and searched everywhere but could not find it. A year or two later the starter went bad, when I took it off, the plug socket fell to the ground. It rode there next to the starter for over 15000 miles.
I just picked this up this week and thought it was for lapping valves. Thanks for verifying that. Mine has a disc on the end with two pins. On the handle it is stamped "No3 Walden-Worcester, Pat Pdg." It is kind of hard to read in the photo because F.L. had to go and stamp his initials on it.