The Kinetic Research Group Grip Panel with Thumbshelf is designed to help you find that perfect firing hand position every time. The Thumbshelf Grip Panel offers a more pronounced thumb shelf to place your finger in an optimal and repeatable firing position. Additional trigger finger rest can also be added and is sold separately. The Thumbshelf Grip panel comes in the standard panel size and is not compatible with a large size LH grip panel. Fits: C-4, Whiskey-3 Chassis gen 3-6, and X-Ray Chassis