There is a tiny spring that has a tendency to fly when you open it up, so make sure you do this were you won't loose the spring. Also, make sure you put the same screws back in the same holes them came from, there are several slightly different sizes, and you can put a larger screw in a smaller hole, it works, but then the smaller screw will fall out of the larger hole. I'd recomend doing one arm at a time so you can use the other one assembled as a guide.