Self-centering tapered-thread Z-axis coupling [v2 tighter]

thingiverse

I've made the changes suggested by @runtimeterror. This gives you something to grip with a 15mm wrench (0.5905511811 inches). Now the nuts start squeezing it earlier instead of exactly when they're at the bottom, mainly an issue on well-calibrated printers. I also removed the through hole in the screw for some reason; printing circles in mid-air rarely works out.