This sliding Y-endstop is attached to the rear (or front) short threaded rods of the Prusa i3 type 3D printers.
The endstop mount consists of a fixed base and a sliding arm onto which the endstop switch is attached. The diameter and the spacing of the rods, as well as the length of the slide and the position of the switch (horizontal or vertical) are all parametrized.
The endstop can be mounted without disassembling the rods. It is first "clicked" into the lower short threaded rod and then rotated along the circular cavity to "click" into
the upper rod. The endstop holder holds quite firmly on its own. But for an firmer hold, it can be clamped between two screw nuts - but then you need to disassemble the Y-frame to insert the additional nuts :( .
The switch plate has screw holes that fit the standard 20x6mm micro-switches which have screw holes which are spaced by 9.5mm. I found it easiest to extend the 2mm holes with a 2.5mm drill bit and then cut an M3 thread into them (using an M3 tap or just a clean cut M3 screw).
The SCAD file is fully parametrized. STL files are provided for 8mm short threaded rods with 20mm rod distance (center-to-center), as well as for 10mm threaded rods with 22mm rod distance. STL files for sliding arms of various lengths and different orientation are also provided. The slide arms are compatible with those of my other endstops, so STL files for further arm variations can also be downloaded from here.
Update 2014-11-18: I have now uploaded one more STL file which has the slide cage offset by 10mm (xoff=10 in the SCAD file). This version is useful when the endstop position is to be directly above the threaded rods, as is shown on the 3rd photo. Other than the initial version, this version doesn't have a "dead spot" above the rod, but the endstop switch can be at any location in front or behind the rear rods that is within reach of the slid arm. Near the rod, it might be necessary to rotate the endstop holder by 180 degrees.
Update 2015-12-13: I have now uploaded two more STL files in which the slide case is lowered by 4mm and pushed sideways out of the rod area. This version might be useful for printers that have a very low printing platform.