The Catch22 clip-on magazine shim can clip right onto your Mil-Spec AR-15 lower receiver for a quick and easy way to shim S&W 15-22 magazines and take up the slack in the mag well. The clip is easy to install and remove and it allows you to use your standard S&W 15-22 magazines in your AR without any modification. With the 15-22 magazine adapters, the S&W 15-22 magazine will work great with the Catch22 V1 or V2 to provide true last-round-hold-open functionality. If you are using a Kriss Defiance DMK22 which already comes with a bolt catch, you can use these adapters to use the 15-22 magazines instead of the Kriss magazines. This can be helpful as the 15-22 magazines are more consistent for bolt-hold-open and they come in higher capacity than the Kriss magazines. One adapter is needed per lower.