AR MAGLOCK Gen 4 - AR-15 (.223 / 5.56) Fixed Magazine Lock and Release Solution (AR MAGLOCK in anodized black components).The Gen 4 benefits:- New set screw on locking arm, allowing for adjustment to ANY receiver width including billet, composite, or 80% non mil-spec receivers.- Allows for "free state" adjustment when traveling outside California. Just reset the set screw to the end of the post and the locking arm will work just like an OEM magazine release button.All AR MAGLOCK locking kits are patented under USPTO patent number: 8,756,845.