Our Radius Corner Block is used to transform the square sidewall hole into a radius hole so it may accommodate a radius window. This particular Corner Block has a 2 1/2" Radius with a 90 degree Angle and is 1 3/8" wide. It has been used in many different RV’s and Motor homes like Fleetwood, Winnebago, Forest River, Thor, Skyline, Monaco etc to allow a radius window. #122 Corner Block.