The screw will be a dum threaded stainless steel rod M6 x 1, turned at both ends to receive the bearings.
The nut will be nylon and threaded tight, so as to have a negative operating play. It is the elasticity of Nylon that will compensate. This is necessary in order not to have backlash.
For the bearings: objective side, a fixed bearing, and APN side, a single bearing.
On this side will be the crank.
Make way for photos (which speak for themselves).