These corrosion-proof 18" PVC Blastgate Dampers are for the construction of exhaust ventilation systems. PVC material compounds used in the manufacture of these duct fittings conform to PVC 1120, ASTM D-1784, Type 1, Grade 1, Cell Class 12454-B. Dampers are furnished with a three position locking pin (open, half open, and closed). Dimensions are 9.25" long, 19.5" wide, and 28" high (not including gate). Gate is 3/16" thick and socket depth is 2.5". NOTES: Fittings are triple bead welded. Pictures are to represent style of fittings only; color is gray.