I've used Kirby belts on my Royal's
A Kirby FLAT belt will work on the Royal. However, the Kirby belt is a bit tighter fit as opposed to the Royal belt. Depending on the model Royal and the exhaust fan size check to make sure the motor isn't getting to warm. A Kirby FLAT belt was to tight for my Royal model 880 and seemed to cause the motor to get quite warm. Yet worked fine on my Royal Classic edition model.
