Might be a bit OCD on needing that thin gap, perhaps.. think about a 2 nut instead?

Of course, the top cap is thicker ,
it has to be internally threaded, lock nut externally threaded and internally tapered,
to compress the collet, as it is tightened down..

http://chrisking.com/tech >> http://chrisking.com/files/pdfs/GripNut.pdf