Round Ducts are manufactured with various seam types. The most common being “Spiral”
and “Double Seam (ACME)”
Spiral ducts are not limited in length, except as required to fit on a truck or elevator or as
needed for the insertion of fitting. Reinforcement rings are generally not required. The use of
Rings help maintain roundness of duct as size gets larger.
In addition to the Spiral seam, there are various other types of seams that run straight from
one end to the other longitudinally, such as Double Seam or ACME joint.