A seam for ductwork has a male end portion integrally formed at a distal end of a duct wall and a female end portion integrally formed at another distal end of the duct wall. The female end portion includes a first fold and a second fold, which define a female groove for accommodating the male portion. A distal end of the second fold is bent transverse to the female groove prior to the male portion being inserted into the female groove.