I have just installed one of Bobby Carvers new thumbrest for the Carver Mount. The rest is approximately .5 square with a mounting surface .345 x .5 in base aluminum and its installed with two screws. The rest is user installed by drilling 2 holes and tapping them to 3-48 thread. Mounting is accomplished by using double sided tape to test for the location that works best with your grip, marking the hole locations then drilling and tapping the side plate. I found the rest to give a more secure location for my left thumb and it was comfortable to shoot with. As to actual improvement I cant make any claims, I have only put a hundred or so rounds through Blue with the rest mounted, but I know the gun feels better. It also allows a better location for your thumb, helping prevent the dreaded magic thumb slide drag.