This is a Pearce Grip , model PG-19.
These Grip Extensions replace the magazine base plate providing better comfort and control by adding approximately 1/2 inch of gripping surface. They do not alter the capacity of the magazine. Fits Gen 3 models 17"18"19"22"23"24"25"31"32"34"35"37"38 - Full Metal Lined Magazines Only.
Features:
High Impact Polymer
Increased Comfort and Control
Provides Magazine Identification