To date the largest measurement I have gotten fromt he valves is .692 Inch's. The largest bore size I have gotten is .6938 but my bore guage will not read that far in tot he bore. Unlike most modern trumpet's this valve engine does not have liners brazed in. The valves ride directly against the bore of the cast valve engine. If I could reach further in to the bore I would feel safer with my measurements that way I would know if their was any hour glassing of the bore. I am working on either getting a smaller gauge set so I can reach in their and measure onthe cheap or getting a telescopic 3 point dial indicating bore guage $$$$ more accurate but the price is much higher as well. I want to know what they where OEM so that as I am plateing I have a goal or a stop point. This way I am not checking them constantly for size. Thanks guys and gals!!!