General three different seams are common in the industry to connect the corners of the ducts: button lock seam, Pittsburgh seam and Duct seam. Button snap lock and Pittsburgh lock can be produced on the Comifo lock forming machines. The Pittsburgh seam shows much better results and c an also be used for a higher pressure.

Whisper-Loc Seam Closer are available in the horizontal or vertical and close pittsburgh seams. Pittsburgh joint is commonly used to join the seams of metal ducts. Seam closing has traditionally been accomplished by manually hammering the margin of the seam against the duct wall (peening). Disadvantages of such peening include the time required and the almost intolerable noise produced.

The latest design in seaming technology is now available. At the Pittsburgh joint, the individual seams are called Pittsburgh seam(pittsburgh lock) and standing seam(right angle flange). On a Pittsburgh joint, the operator pushes the standing seam into the Pittsburgh seam, fastens them to each other and closes the joint on a seam machine.