Parametric z leadscrew nut clamp for Huxley

This is a parametric part for Huxley and for Mendel variants (its function is served by part of another assembly in a standard Mendel. For Huxley, it replaces two parts of x-axis-clamp 4off.stl, should print in less space than one of the original parts, and (like my y-bar clamps) requires no screws! It has the added advantage of functioning as an anti-backlash nut, and was inspired by the anti-backlash nuts in the Prusa Mendel, but it uses the springiness of the printed part instead of a (vitamin) coil spring.

This part is untested, as I'm working on my printer at the moment.