Newman is correct; they need to be vapor metalized.
It IS going to cost you a bunch to do this; that is for sure. Plus it typically takes a couple weeks to do them.
The thickness of the coating is angstroms in thickness; it will have NO effect on thread or spline engagement.
I don’t know of any place locally that does this. I have stuff vapor metallized for work, but our places are in the Boston area, and in OH, and neither do TI coatings.
Expect to pay a DAMN high price for this; the process and materials involved are NOT cheap.