You may want to try using a better grade of machine screw/bolt to avoid having this kind of problem. I have gone through every sort of hardware since getting seriously involved in R/C from stainless steel, to titanium, Tonys screw, Hexhead screws, as well as all grades of black steel screws. The best screws I have found are the grade 12.9 hard steel screws that you can find at a few hardware suppliers around the globe. The link below shows you just some of the screws I now use, and I have yet to strip or break one of these. If you want the best results, then you have to use the best tools and hardware to hold your expensive toy together. Lito turned me on to BoltDepot.com a couple of years ago, and I have not been disapointed yet. I have about $1000 in hardware from them in my R/C storage bins, and I have changed out everything on my trucks using their 12.9 grade screws. Everything looks clean, and everything works the way it should. These are hard steel and if you break these then you are torquing things down way to hard. If so start using a torque screwdriver to measure and torque your connections to the right level.
http://www.boltdepot.com/Metric_sock...m_x_0.5mm.aspx