I’m assembling my X-Carve and the instructions say to put the lock washer on the screw before putting it through the switch hole, then putting just the nut on the other side of the plate. Is this really right? It seems to make it harder to get the nut snugged on. I’d think putting the lock washer on just before the nut would make more sense. I’ve double checked the images in the assembly instructions and they clearly show putting the lock washer on the head end of the screw.
I don’t think it matters that much, unless the head of the screw would pull into the homing switch without the lock washer under it.
I put mine together the way the instructions indicated. No problems, but I used loctite on all threads.
I have mine under the head of the screw, as the instructions show, and it has worked just great so far. Don’t worry 'bout it, just pop 'em on and keep going. Works great. 
I didn’t bother with them, I used a bit of superglue and so far they are permanent.