Abstract: A rolling shutter system employs a variable efficiency bi-directional drive mechanism which permits easy and quick raising of the rolling shutter while protecting against self-lowering of the shutter by reason of its own weight. The system also employs a novel operator for the bi-directional drive mechanism which is characterized by an easy and comfortable to grip bead string which also is attractive in appearance. The bead string is trained about a sprocket wheel, and an overload slip clutch is provided between the sprocket wheel and worm gear drive to limit the amount of force that can be applied to the bead string during raising and lowering of the rolling shutter. Also provided is a novel shutter travel limit and locking device, a novel valance construction and a novel through the wall shaft assembly.