Just purchased the NN3 with the RD8. The "picture" instructions that arrived show and talk about the NN5 w/R-D8, but the unit is an NN3 with RD8 I assume. My tripod has a 1/4" screw mount on the quick release plate and the enclosed 3/8 to 1/4/ adapter screw goes into the RDR OK, but the tripod quick release screw won't go into the adapter (just a couple of turns). If however, I just try the adapter, and screw it on by turing it over, it works. But of course then it won't go into the RD8. Soooo, at a standstill.
P.S. I did download and print the NN3 User Manual, and watched all the relevant videos.