This is a Hogue known as the Rubber Grip, model 79080.
Precision fit for the Ruger 22/45 MkIV
Features:
Color: Black
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
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