In theater, a brace is a sliding piece of wood or metal with a 'butterfly' winged nut to make it longer or shorter to fit the flat used to stabilize a flat set piece such as a flat. Wikipedia

A stabilizer for a piece of scenery Wikipedia Disambiguation

A piece of material used to transmit, or change the direction of, weight or pressure; any one of the pieces, in a frame or truss, which divide the structure into triangular parts. It may act as a tie, or as a strut, and serves to prevent distortion of the structure, and transverse strains in its members. A boiler brace is a diagonal stay, connecting the head with the shell. Wiktionary