Sliding X-Endstop for Jonas Kuehling's Improved Prusa X-Ends

As much as I like the design of the RepRap/Prusa/Mendel type 3D printer, there is one thing I never got happy with: these tiny endstop holders that attach to the smooth rods! These are quite fragile and tend to break if you fasten them too much ... and if you don't fasten them tightly they easily move around by the slightest touch.

So my goal was to design new endstop holders which do *not* attach to the (usually greasy) smooth rods, and, thus, are less prone to being moved inadvertently.