This arcane contraption is a transom operator, and it’s used to open and close the ventilation window above a door or larger window without the need of a pole and hook (or a stepladder). You might come across one, or parts of one, in a secondhand shop, likely labeled a “whatchamacallit.” If you want a reproduction that works, you’re in luck: several companies offer them in steel, cast iron, or brass. This one from House of Antique Hardware can be used with transoms hinged top or bottom; with all mounting hardware, $159.90 in solid brass. They also supply ornamental sash locks and other unusual window and door hardware. (888) 223-2545, houseofantiquehardware.com.