Wikipedia
Crémone or "Crémone Bolt" is a type of decorative hardware used as a locking device to fasten a pair of swinging windows or casement window. A knob or lever handle is linked by a rack and pinion gear to a pair of half-round rods or "surface bolts" which slide over the outside surface of the door or window and extend into sockets at the head and sill of the opening. The gear mechanism operates the two vertical rods at the same time; one rod extends up into the door head, and the other extends down into the door sill. It is similar in appearance to an " espagnolette" lock, but uses a half-round rod.
Shown from the backside, the parts of the crémone bolt gearbox (1) includes the lever or knob (3), which rotates the pinion gear (4), engaging the pair of rack gears (2), which then push the two half-round bars (5) upward and downward at the same time (only the bottom bar is shown), into the sockets.
Usage examples of "cremone".
Moving quickly, he twisted the lever of the cremone in the center where the windows met.
Having satisfied himself that there was no one in the bedroom, he slid in the blade and pried the lock, then worked the cremone open.