Delrin nuts. Doesn't Lee make/sell them? Very easy to make yourself I would have thought, lump 'o delrin, 6.5mm drill, M8 tap.

I think by using M8 nuts and preloading them in the way you are doing will lead to wear on either the nuts or screw and quickly too. When using threads in this way, you really need to have the nuts to be of softer material than the thread. I think you will find the most likely scenario will be that your leadscrew will seize and scrap both the screw and the nut even with lube, BTW, don't even think of trying it with Stainless nuts/screws.

Make some delrin nuts!:p

That's what I'd do anyway, no doubt I'll get shot down now by everyone who's done it your way for years:D

Jeff.