Is Uni larger or just round whereas the Danville is flat? If you mic the Danville across its width would it mic out larger then the Uni?
"Global Flyfisher thread table .041 mm .....0016 inches i doubt it" - Agree
".0029 inches it does not look that much smaller than 6x tippet" - Well, 6x tippet would be .005 inches
"Thread Exchange says 135 denier polyester thread has a diameter of .0047 inches this is a generic thread for comparison" - Have no idea but that's very close to what the diameter of 6x is supposed to be.

Allan