It will easily fit into your break open shotgun barrel and accept any 22LR or 22 Short ammunition.  After firing simply remove the adapter and tip upside down to remove the spent 22 shell, or use your finger nail to grab and remove the shell while the adapter stays in your gun.  The  wide groove cut in the face will not only allow you to easily remove a spent shell but also provides a recessed clearance area for your firing pin.   Adapters that don't have this recessed area (or recessed area in the wrong spot)  do not provide the proper clearance for your firing pin and may damage your shotgun.