Headrail

The headrail is the horizontal housing at the top of a blind or shade that contains the lift mechanism, the roller tube, or the tilt hardware, and it is the part that fixes into the mounting brackets. Its depth is what sets the inside-mount depth requirement, and its finish (an exposed rail, a fabric-wrapped cassette, or a valance cover) is largely cosmetic. On motorized shades the headrail also houses the motor and battery. When a spec sheet quotes a mount depth, it is quoting clearance for the headrail — so read that number against your shallowest measured depth before committing to an inside mount.