A cremone bolt is a type of hardware that uses surface-mounted vertical rods to secure a door or window. Cremone bolt sets are similar to modern flush bolts, but are often much more ornamental than other varieties of modern hardware. They secure the door only along the top or bottom of the opening, while flush bolts generally secure both the top and bottom of the door. Because of their relatively low level of security protection, cremone bolts are often used more for aesthetics than for keeping a building secure.
The most common application for a cremone bolt set is along the interior side of a pair of French doors. French doors are often used at patios and balconies, but are also found within the home when certain styles of decorating are used. These bolts may be used on both doors within the pair, or only on the inactive leaf. A cremone bolt set may also be installed horizontally across a casement window to keep the window secure.
Cremone bolts include two interconnecting rods that run the entire length of a door, or entire width of a window. At one end of the rods is a bolt that projects into a floor plate or into the frame itself. A knob or level sits at the point where the two rods meet. When users turn the knob, the bolt lifts up out of the floor plate. If the knob is turned again, the bolt retracts back down into the floor to lock the door.
Most cremone bolt sets can only be operated using the knob or lever where the rods intersect. Some specialized varieties feature a traditional lock cylinder that can be locked and unlocked from both sides of the opening with a key, though this model is fairly uncommon. Buyers can choose from a variety of finishes and designs, with brass and stainless steel among the most popular finishes. Many cremone bolts are shaped into elaborate designs and patterns to give doors an ornate appearance, while others are more simple and modern.
The primary benefit to cremone bolt hardware is its traditional, distinctive look. These locks are also easy to operate, and there is typically no key to keep track of. Because they are surface mounted on the door, they are simple to install and don't require extensive preparations in the door or frame.
At the same time, these locks provide fairly little security, and should be combined with more effective locking systems to keep a building truly secure. Unless the cremone bolt has a cylinder, it can only be operated from the inside, which can make it inconvenient for some applications. These locks can also be difficult to maintain as users may accidentally push the rods out of alignment during everyday use.