Dimensions are in mm (in.) × = not allowed; any length of duct of this size INTRODUCTIONDUCT COMPONENTSDUCT CLASSIFICATIONVelocity ClassificationPressure classificationDUCT MATERIALSMetallic DuctsNon Metallic ductsDUCT SHAPESRound DuctsRectangular DuctsOval DuctsSUPPLY