A stage truss is a piece of stage equipment which is designed to support lighting, screens, and other accessories. Stage trusses may be permanently installed, as in a theater with a trusswork system suspended from the ceiling, or they may be movable. Stage trusses are used in a variety of settings, from public parks used for concert series to opera houses, and they are constructed by a number of different companies, several of which are capable of fabricating custom trusses for specific applications. Classically, a stage truss takes the form of a box truss, which may be welded or bolted to other trusses to create a stand, or may be designed to be suspended from rigging in a building used for performances. The structural elements of the stage truss can be used as attachment points for lighting instruments, pulleys for moving performers or scenery, special effects devices like bubble makers, and monitors or screens. Stage trusses also commonly provide support for the extensive wiring and cabling used in performance, from wiring associated with individual lights on a stage truss to microphone cord. Also known as lighting racks, stage trusses are sometimes visible in the performance. People who attend outdoor concerts may have noted stage trusses over the stage and along the side of the stage, and the design of indoor venues may also allow patrons to see the trusses. These devices are usually installed with redundant safety precautions to reduce the risk of an accident caused by a falling or improperly secured truss. Since stage trusses may need to bear a great deal of weight, safety is important at the time of installation. Portable truss systems are often available for rental. A portable stage truss can be used for tasks such as setting up racks of lighting at an outdoor party, supporting a tent for a backyard wedding, or providing structural support for a booth at a trade show. Companies which specialize in events often keep a number of portable trusses in their stock and they take care of installation on site. The truss will usually have a load rating which should be carefully noted. For people and organizations who have a routine need for a stage truss, companies which manufacture theatrical equipment can be good sources for new and used trusses. Used trusses are often a great choice, because they are less expensive than new trusses and they have usually been well maintained, so they are in good shape. If a custom size or configuration is needed, the manufacturer may charge extra for custom fabrication, especially if none of its standard components will fit.