These corrosion-proof 18" CPVC Socket Flanges are for the construction of exhaust ventilation systems. CPVC material compounds used in the manufacture of these duct fittings conform to Type VI, Grade 1 CPVC, Cell Class 23447 as described in ASTM D-1784. 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. Maximum service temperature is 200°F. NOTES: Fittings are triple bead welded. Pictures are to represent style of fittings only; actual color is light gray.