Pre-cut (never installed) marble fireplace surround trim. Cut to wrong size. As cut, this trim will cover a fireplace opening of 30in. x 30in. but can be cut to suit smaller dimensions. As cut the outside dimensions are 421/4in. x 421/4in. and the inside dimensions are 303/8in. x 303/8in. The material is 13/16in (20mm) thick.