What is the Longitudinal Seam and Transverse Joint in Rectangular Duct?

/ HVAC Ductwork 101 / By /

What is the Longitudinal Seam and Transverse Joint in Rectangular Duct?

Longitudinal part of Rectangular Duct is the length, while Transverse part is the width

  • SMACNA refers to the Longitudinal as a seam and Transverse as a joint.
  • A seam is securing together two longitudinal oriented edges of duct in the direction of airflow.
  • A joint is the Transverse connection that connects the end of one duct section to another.
  • The Longitudinal Seam in Rectangular Duct is either a Pittsburgh Lock or a “Snap” Lock.  Both types are formed on a machine that takes a sheet of metal and rollforms a profile on each of the flat edges — a Male Flange on one edge and a Female Pocket on the other edge.
  • The Transverse Connection options are Slip & Drive, Ductmate, or TDC/F.  Of these, only Ductmate is an entirely separate component. Both Slip & Drive and  TDC/F involve rollforming a profile on the edge of the metal.