Don't know if this translates to the 3, but on a TR6, the knurled nuts for the tach/speedo and the oil gauge look identical, but aren't. Oil gauge nuts are 8-32, while those on the tach/speedo are 3B.
Thanks for the info
.Any idea what size the small screw is on the back of the panel switch rheostat? I missing one screw that would attach a wire.