This endstop is designed to fit the Z axis on Prusa i3 without any impact on the mechanical structure. Just fit and adjust.

It is mainly composed of two components: a support clamped to the left vertical smooth rod that holds the miscroswitch,
and a bracket that hold the adjustable plate attached to the free threaded hole of the X axis stepper motor.
Also in this construction I made the 3D model considering the metallic nuts co_bonded in a plastic shell, so remember to pause the printing at the last opened layer, insert manually the nuts in place (as shown in the attached picture) and then exit from the pause.

Due to the fact that I got problem finding M2,5 screws I slightly enlarged diameters on endstop to allow the using of M3 screws.