Measuring bore size and Conn tubas questions

[PKeen]

Where is the bore size of a tuba generally measured?
What were the bore sizes of the old Conn 2J and 3J horns?

[WilliamVance]

Bored is usually measured in the valve section. The tubing is cylindrical in this section and then gets larger(conical)after the valves. Sometimes the 4th or 5th valve will have a larger bore. On Conn 2J and 3J I think the bore is .656 since I think they are generally the same frame, just different valve configurations, as the 11J/12J series and Conn used the same tubing stock on this whole line.

[Lew]

To be a little more specific, bore is typically measured at the inner diameter of the second valve inner slide.