AHHH!!! the screw lock system that comes stock on the makergear M2 is anything but fun to adjust ;)
Anyway this solves that :) All you need in addition to the stock bolt and nut is a small spring that fits over the 4mm screw and is between 10 - 20mm long.
You pretension the spring a little, then insert the nut in the top - constant pressure is then put on the screw holding it in place, fine adjustment is possible with just your hand :) and the nut will never turn because of the spring tension and the arm which locks the screw precisely to the side of the linear bearing.
This will work great with the stock mechanical switch, but for even higher end stop repeat-ability you should consider buying a $2 optical end stop switch like I have from ebay, see my other files for the 3d printable mount. This combo makes ultra consistent bed adhesion possible.
I also recommend putting a drop of Vibra-TITE 213 VC-3 which is a non-drying thread locker.
Optical Endstop: http://www.thingiverse.com/thing:1195834
Youtube video covering my various Makergear M2 Mods:
By - http://www.easybotics.com/
And - http://hilo90mhz.com/