Originally Posted by
Scooper
This is a seat lug like the one Cynikal is describing. The ridge is 0.8mm thick on this one, and the seat tube butts up against it.
Here is the view from the top of the lug with a tube inserted and butted against the ridge.

Yup. that's it. Clearly a picture is worth a 1000 poorly chosen words.
__________________
I'm not one for fawning over bicycles, but I do believe that our bikes communicate with us, and what this bike is saying is, "You're an idiot." BikeSnobNYC