Ahhhh, 39 centimeters. For some reason I was remembering something like 39 inches or so, rather than centimeters.
And I wouldn't necessarily count the secondary or primary frame in the hull thickness because that frame isn't everywhere. Primary frame is probably something like a big honking beam every 50 meters or so, while the secondary frame is probably every 10-20 meters or so...for example, a secondary frame is probably part of the living quarters wall or partition between compartments, hiding the secondary from the occupants of the ship, as opposed to a big beam that you might find running down the centerline of your living room or unfinished basement. I guess I'd have to take a closer look at the TNGTM to see if they have a view of how the framework ties together or how much space is between the frame members, but going off the top of my head without any caffeine this AM, this is how I picture it.
No worries on nitpicking, Graffy. That's why we're all here, and it's fun.