The mounting plates that come with the OpenBuilds "End Stop Kit" are crap.
* Either you force the M3 bolts through the 2.5mm end stop and find no place to fixate them in the unthreaded 3mm holes in the plate
* or you thread the M3 bolts through the plate and fixate them in the end stops...but then you have the head of the plates between the plate and the aluminium profile and things jsut don't aline flat.

I present 2 versions.
* The "thread cutting" version assumes you 3D print the part and cut an M3 thread into the mounting holes for the end stop.
* The other version has additional space for the head of the M3 bolts.
Both are also properly sized for the mounting holes of the end stops and don't use long holes to adjust to unknown sizes. The end position of the arm is always slightly beyond either the right, upper or lower side of the plate. (whatever position you choose for the switch)

Note: In any case you are advised to tap an M3 thread into the end stop first. The holes are 2.5mm and forcing an M3 bolt through it, like obviously planned by OpenBuilds, may damage your end stop.

Blog posting:
https://marcuswolschon.blogspot.de/2017/01/fix-for-broken-openbuilds-end-stop-kit.html