This is as close as I can tell you. The metal in my TR3 appears to be 20 gauge. This is also the gauge that is used on the patch panel that I recently bought from Roadster Factory ( which came from England). To be sure what you can do is to obtain a measuring device to measure the thickness of your metal that you remove and then use that to go buy a replacement piece of metal.
I found that 20 gauge seems to be about .034" and 22 gauge is .030".
I am assuming that the metal thickness did not change from the TR3 to the TR4.
Hope that this helps.
Charley Fitch
