Rails are the horizontal pieces of the door. Rails are important to consider for hardware mounted to the top of bottom of the door. Door hardware such as concealed or surface mounted closers as well as kick plates or armor plates must have enough room to be installed inside of or on the surface of the rails of the door. If the hardware requires a mortise in the top or bottom of the door be sure that the dimension of the rails will allow for it without compromising the structural integrity of the door. Generally a rail is a minimum 1-1/8″ wide or can be as wide as 5″, depending on the application. For doors with lites, the top rail should be no less than 6″ for surface mounted closer and, depending on the hardware, the rail dimension may need to be increased. The bottom rail is usually at least 10″ wide to meet ADA requirements for a smooth surface on the bottom 10″.