Colnago C40 Mapei Frameset, CK H/S, Colnago Seatpost

@gaston that’s actually my bike there in the photo. Non b-stay c40.

It has a DA7410 27.2mm in it with a shim. Tube size is 28mm.

That model is about 2000/2001. I’ve a ‘96 non b-stay too with the downtube bosses (same colour way as yours) and that’s a 28mm too.