This is a Hogue known as the HandAll Beavertail Grip Sleeve, model 17023.
Precision fit for the following standard frame GLOCK Generations 1" 2 & 5 (9MM" 357 SIG" 40 S&W" 45 GAP): G17" G17L" G17 MOS" G18" G19X" G20" G21" G22" G24" G31" G34" G34 MOS" G35" G40" G41" G45
Features:
Color: Flat Dark Earth
Gentle palm swells fit comfortably in hand
Finger grooves naturally position fingers for optimal grip
Textured with Hogue's famous Cobblestone pattern for increased comfort and grip
Beavertail cushions the hand on recoil and offers increased hand comfort higher on the grip
Made from long lasting durable thermoplastic elastomer that ages gracefully for years of service
Designed for a tight and secure fit engaging with the texture and contours of the firearm's frame
