Dovetail seams are practical for which purpose?

• A. substituting for lap seams.
• B. turning around elbows.
• C. connecting round pipe or a collar to flat metals.
• D. connecting ducts.

Answer: (C)

Dovetail seams are used because they create a secure interlock that lets a round piece fit neatly into flat sheet metal. By shaping the edge on the round pipe or collar and matching it with a wedge-shaped cut on the flat metal, you can slide the pieces together and have the joint lock in place. This provides both strength and a good seal without needing lots of fasteners, which is ideal when joining round ducts or pipes to flat metal surfaces.

The other uses aren’t as well suited: lap seams are for flat sheets edge-to-edge, not for attaching round components; turning around elbows requires curved geometry and special elbow fittings rather than an interlocking dovetail; and while ducts can be joined in various ways, the dovetail’s main advantage is the round-to-flat connection described.