These tapers are commonly seen in ductwork systems. They are simple in that they only reduce in size in one dimension, and are also offset to one side. This means three of the four sides are flat. The length of each taper will be determined by the slope angle; ductwork specification DW144 stipulates a slope angle of no more than 22.5°. We fabricate them with a slope angle between 20° and 22.5°.