Dust Duct is the total system of pre-engineered, welded metal ducting and fittings are used for dust control work. There are different types of fittings in a full range in all diameters by half-inch increments. These types and sizes cover almost 100% of the requirements for air pollution and dust control systems, excepting very unusual or extremely large jobs. Dust Duct fittings such as transitions and tapers are made with short straight-end collars to permit joining by standard compressor couplings or flanges. Collar lengths are depending on diameter. Flared straight pipe and ells are normally supplied with one flange welded to one end, and the other flange loose so it can be welded in the field so both holes can be aligned to fit as required. Other fittings may have all flanges welded on. Note that longitudinal seams are normally centered top or bottom. Flanges are welded to the part so one bolt hope is in line with the seam. Fittings are mace with collars, even when flanged.