Mild Steel Zinc-plated; available in Vent or Safe Seal.
100 - 224 Dia are pressed construction; 250 Dia and above are fabricated in segments.
Bends are 'male' and slip inside spiral duct. A female coupler is required to join fittings together.
Throat radius equal to half diameter.
Diameters 180, 224, 280 and 600 are made to order, on a minimum 14 working day lead time.