Carlon B121BFBRR is a floor box kit that can be installed on a joist or subfloor. It can be used for new or old work installations, and it comes with both a new work bracket and an old work bracket. The new work bracket can be installed on the floor joist below a 3/4 inch subfloor, or from the underside of the joist. The old work bracket is used for installations where the new work bracket cannot be used, such as in tight locations or cut-in situations. The box has a two (2) hour fire classification and is listed as a floor box by Underwriters Laboratories.