This colonial design backband mounts to the outside edge of 5/8″ builder casing and ads width and depth to the casing. It is rabetted to accomodate any 5/8″ thick casing and is great for when people upgrade to a thicker base, but not yet ready to change out the trim.  This added backband to the trim will accommodate a thicker base and the shoe can but into the backband as well for a better fit and finish look.