These corrosion-proof 18" PVC Socket Flanges 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. All Socket Flanges are 3/16" thick material. 18" flanges have 20 bolt holes that are 5/16" diameter with a 20.5" diameter bolt hole pattern. Overall dimensions are 22" diameter and 4" long with a 2.5" socket depth. Service temperature is 33°F to 140°F. NOTES: Fittings are triple bead welded. Pictures are to represent style of fittings only; color is gray.