These parts represent your choices for 922(r) compliance with the Benelli M4 shotgun. If you don't see the part here, then it doesn't count towards compliance. You'll need 3 parts below for increased magazine capacity and no skeletonized stock, and 4 parts if your gun has the skeletonized stock, whether or not it collapses and whether or not you increased mag capacity. 4 is the most you'll need, and after that you can modify your gun however you'd like, as 922(r) only deals with the magazine capacity and skeletonized stocks. See here for more on 922(r).