This is a X-GRIP known as the Mag Spacer, model BRPX4SC.
The XGBRPX4SC XGRIP adapts the full size Beretta PX4 magazines for use in the sub compact PX4SC pistol" incorporating the larger magazine into the sub compact's grip" increasing the capacity and grip area.
Features:
Improved Comfort, Control, and Accuracy
Increased Capacity
Secure Fit
