Adjustable Z endstop using LM8UU/LM10UU

This adjustable Z end stop holder uses bearings to provide for rock-solid operation. I've tried many of the other designs, but they all have too much play in them to achieve any accuracy. Since I was looking for adjustment along a smooth bar, I decided to try mounting to an LM10UU bearing (I have 10mm z bars). I use a second bearing to maintain alignment.