out of the sprocket hole in the door if the lower tooth did not unload the upper tooth the upper tooth would hook on the sprocket hole and the mechanism would bind the edge of the sprocket the face that slides along the inside of the sprocket hole we will use the term u201c flank u201d the preferred embodiment is that the sprocket be punched out of the same sheet metal type of material as the door itself their hardness and characteristics should be the same or nearly so the material should be a hard material such as steel or galvanized steel and only due to the requirement that the door operates less frequently and not continuously can it be trusted that the sprocket and sprocket holes do not wear detrimentally to the functionality other materials such as stainless steel or softer materials such as aluminum or brass or even polymer materials could be made to function well as alternative embodiments of this invention some materials could be cast molded or formed especially plastic materials and would still be part of the described invention the spacing of the holes in the door should be equal or nearly equal to spacing of the teeth not at the root and not at the crest but in between we could use the terminology major diameter diameter of the sprocket at the crests of the teeth pitch diameter diameter of the sprocket at the mid point of the teeth minor diameter diameter of the sprocket at the root of the teeth the spacing is.