Battle Arms Development has pivot and takedown pins that work perfectly, and come with the detents and springs. Their bolt catch also works with the M5s, but don't come with the detent and spring. Their BAD-ASS PRO 60* safety is the best on the market, comes with detent and spring. After that, you're complete, minus whatever trigger you desire, grip as well, and a bolt catch detent and spring, and whatever you want to run for a mag catch - any AR15 mag catch will work. Your bolt catch is threaded, and the allen bolt should be in the lower already. On your M5 upper, the forward assist is threaded, and the bolt will be in there.