I am not sure what you are asking. If you are adding aftermarket guages to your dash, the diam. of the guage is in the installation pkg. you get with the guage set. For me an under dash setup is the way to go, but I like to keep the dash as near origional as possible. If you are building a street rod or somthing custom then I see your need for guage size.

I didn't do it, no one saw me do it, you can't prove anything! "Bart Simpson"