This is the KRISS Vector 9mm 40-round magazine. 

Extend your capacity with this 40-round KRISS Vector magazine that is built on a genuine Glock magazine.   

Pairing the reliability of the OEM Glock magazine with the additional capacity via the KRISS magazine extension results in one close-to-perfect magazine. The only thing that could be better is even more rounds! Best of all, you can use these with any firearm that is compatible with Glock magazines…versatility at its finest!

From extending your range time to maximizing your zombie defense, these extended 40-round magazines are just what you need for your KRISS Vector!