Standard Headrail: refers to the most commonly used option unles the window is too large to be covered by one blind. 2 and 3 on 1 headrail:We recommend splitting very large windows into 2 blinds on 1 headrail or 3 blinds on 1 headrail to avoid operation issues. Each blind has its own set of controls and operates independently. You may choose the size and control position for each blind. Valance is included and it’s made to cover the total width ordered. You may choose to order a single blind, however this will void the manufacturer’s warranty.