-
Looks like this. Hole is around 3.5x1.5cm and 4.5cm deep.
Comes with a clip on cover like this that I would cut to put the junction box into. If it all can fit.
1 Attachment
-
The bar end junction box comes with a plate for storing it in downtubes with holes in frame like this.
-
Found some bits and pieces while I was tidying up, don't know if this helps you at all. The square bit is a blanking plug for the plate, and it's the same size as the end of the junction box. I can't measure how long that is because I'd have to unwrap my handlebars. It looks as though the hole in your frame isn't wide enough.
Got any photos? Pinarello definitely mount it here and an increasing number of other manufacturers.