This is a Pearce Grip Extension known as the Grip, model PG-2733.
These units replace the magazine base plate and internal floor plate. They will add two rounds to the Glock M26" one round to the Glock M27 and M33 and no rounds to the Glock M39. These units will add 5/8" additional length for better control and comfort.
Features:
High Impact Polymer
Increased Comfort and Control
Provides Magazine Identification