This is a Hogue known as the HandAll Beavertail Grip Sleeve, model 17701.
Precision fit for Ruger Security 9 Standard models
Features:
Color: Olive Drab Green
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
