The patented 1 piece XGRIP adapts the full-size 7 or 8 round metal floorplate magazine for use in the compact, incorporating the larger magazine into the compact’s grip, and increasing the gun’s capacity to 7or 8 rounds. So basically the Xgrip adapter goes over the an 8 round mag so it fits flush in a compact frame.
The 2 piece XGRIP snaps over the 8 round magazine plastic floorplate. No tools are required. Once installed, the XGRIP completely encloses and protects the extended magazine and floorplate. Compatible only with the Act-Mag / NOVAK and Mec-Gar (model 17-7PH) 1911 brand magazines. For this one, I'm guessing the adapter helps cover the bottom section of a 10 round mag that hangs out of a full size frame.