TL;DR- Openbuilds Parts Store M5 x 20Mmm low profile screws have a head dimension to large for the C-Beam aluminum end plates and may bind in the hole, preventing normal removal of the screw. Consider sourcing other screws or reducing the diameter of the provided screw head. During a recent build of a c-beam machine I found that the M5 20mm low profile screws I received had a significantly larger head diameter than the others. Other screws I measured were on average .011" smaller in head diameter of my 20mm screws. Unfortunately this means that the 20mm screws head is actually larger in diameter than the couterbored hole in the C-beam end mount plates. This causes the screws to bind around their perimeter when inserted as instructed. This binding may prevent the screws from being removed because it can lead to stripping of the hex socket. During my build I had to remove the plates to correct an error. I found that one screw on each plate was bound and could not be removed without stripping the socket. Interestingly enough you could actually see on the sides of the hole how the aluminum had been deformed by inserting the screw. (A slight crater like ridge that could be seen with the correct lighting). I was able to remove the plate by removing the lead screw an the other 3 screws in the plate, then rotating the plate the unthread the screw. I suggest that if you find the screws not seating properly in the aluminum plate, that you either get new screws or possibly attempt to reduce the diameter of the screw before using. I am not sure but its possible that a drill combined with a file or sand paper could remove enough to correct the fit. If you don't, you may find yourself in my shoes with a near permanent connection that can't be easily removed without damage. I should note that I contacted the Open Builds part store about the issue a week ago and they have thus far failed to provide any response except "We'll remind the person responsible to get back to you". Very disappointed with the lack of customer service in any shape or form. If there is this much variation in screw head diameter I suggest that the design be modified by increasing the size of the counterbored holes to account for variation in the screws. I ended up purchasing more screws to replace the damaged ones and will likely take a little off of the diameter using a lathe. Good luck! And hopefully you have a better CS experience with open builds than I did. P.S. This is my 3rd CNC router, the first being a Shapeoko 2, and the second CNC Router Parts 4x8 Pro. So far this thing seems WAY more robust than the Shapeoko 2, very excited to get it up and running.