Springfield XD4545 : Caliber : 45 ACP - Capacity : 13 Rounds - Material : Stainless - Fits : XD & XDM 45\'s.Replacement magazines for the XD(M) series of pistols. Some come with a sleeve that slides down over the top of the high capacity magazine and fills the gap between the bottom of the grip frame and the base of the magazine. The #1, #2, #3, tells you which backstrap it is compatible with. #1 is small, #2 is medium, #3 is large.