Please look at pictures above for measuring explanations. AVAILABLE AS OVERLAP OR INSIDE FIT- FOR FIREBOX OPENING SIZE: For measurements up to 44"W x 31" H see price above. For measurements up to 50"W x 39" H, add $135 to the price above. For all other sizes, please call for a quote. The Heritage is Thermo-Rite's first welded steel frame enclosure. The frame is made out of 1/4" x 2 1/2" on 1-3/4" steel plate. The doors feature Thermo-Rite's rugged self aligning hinges and are available with bifold tracked or bifold full-swing trackless designs. The Heritage is an welded steel enclosure with either a 1 3/4" or 2 1/2" wide frame. It is available as an overlap or inside fit. The maximum overlap for 1 3/4" frames is 3/4" each side, 3/4" top with and without mesh. The maximum overlap for 2 1/2" frames is 1 1/2" each side, 1 1/2" top with and without mesh. The inner return of the frame will extend 2 1/2" into the opening. "Wow! My product arrived after three days. Thanks for the fast shipping, I am glad I ordered here. My friend ordered  from a different site and it took six weeks for the item to arrive!!! Keep up the good work." Mary Clarke, CA