The Springer Precision aluminum locking floorplate is for use with our Rock Island Armory .25" basepads.  Specifically, you will need a locking floor plate if your mags do not have the standard factory floor plate with the round locking nub in the middle.  If you have the rear clip-on style locking mechanism, then you will need this part or you will not be able to lock our basepads onto your magazine tube.  This is available separately, or as an add-on option from the .25" basepad page.