Originally Posted by
vintage cellar
Thats a Walter brand CS60 head tube lug. The adjusters are M5, not M4. It looks smaller because of the paint in there. Gently and carefully run a tap in there and you'll be set.
That would certainly be good news since I'm still waiting for my number 19 bit to arrive so I can tap to 5mm. Unfortunately there is no paint on the threads in the hole and my 5mm tap will not even start in the hole. The short reaming section on the front of the tap brings out small flakes of metal and leaves behind a shiny metal surface at the entrance to the hole.
Perhaps they changed the lug design early on when they decided 4mm wasn't such a good idea.
Brent