Shims on Aero enhanced? I’ve set up a few, and they didn’t come with shims. I thought that was the point. The nut is below the port for the gas tube, so you just torque it down, but on the M4E1 there’s a special wrench so don’t forget to buy that). You do have to use their hand guards, though, but that’s ok with me. In my experience, they take about 15 minutes to set up, and they shoot great. Not fiddling about with shims/timing is wonderful. The only reason I’ve bought anything else is to have a particular setup (Daniel Defense and KAC).