If you have an makerfarm prusa i3 8" then you can use these parts. You need a servo Hitec HS-65HB Mini-servo and you can use a standard microswitch. For installing and adjustments this autolevelling i used the blog from zenmaster: http://zennmaster.com/random-things/auto-bed-leveling-for-the-makerfarm-prusa-i3-part-1-assembly-and-basic-setup. And the reprap forum about auto levelling. I also put there my changes to the config.h file and the marlin_main.cpp.