This is a X-GRIP known as the Mag Spacer, model HK2000SK-P30.
This XGRIP adapts the HK P30 high capacity magazine for use in the P2000SK" incorporating the larger magazine into the P2000SK's grip and increasing the gun's capacity to 15 rounds in 9mm and 13 rounds in 40 cal.
Features:
Improved Comfort, Control, and Accuracy
Increased Capacity
Secure Fit