Good simple design. On suggestion to hold the nut in place would be to print a small tube that can be inserted after the nut, from below. The tube can be glued. The thing is so small that it can be printed again if something goes wrong with the glued tube.
I have now calibrated my kossel XL very nicely. One big advantage with this is that it takes effect during print. When adjusting the end stops, the printer must home between adjustments, so not possible during print.