Our Extruded 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 3" Radius with a 90 degree Angle and is sold in 1 Foot lengths. This corner block can be cut down to the correct wall thickness. 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. Extruded Corner Block.