Extrutech Item# CB1720, 3 1/2" wide, Rigid Door Frame Extension for CB1700 our rigid utility door frame, is of an exterior grade, hard, dense, rigid pvc, with a smooth surface. Fits CB1700 3" door frame profile for a 6 1/2" wall thickness, use for 1 3/4' thick door panels, is 3 1/2" wide x 3/4" thick. Cut with standard power saws. Assemble with #8 x 1 3/4" pan head screws and construction adhesive, is available in 7', 14' and 18' foot lengths, with a weight of 1 lb per foot. Can be ordered as stick lengths or 3 sided frame sets ready for assembly.