What is the recommended width and gauge for band iron strips used for ducts over 18 inches?

• A. 2-inch strips of 14-gauge band iron
• B. 1-1/2-inch strips of 16-gauge band iron
• C. 1-inch strips of 22-gauge galvanized iron
• D. 3-inch strips of 18-gauge steel

Answer: (B)

For larger ducts, you need a band that has enough width and strength to hold the joint securely without adding excessive weight or making installation difficult. A strip about 1-1/2 inches wide provides ample surface area to distribute the fastening load along the seam, reducing the risk of the fasteners pulling through the duct edge. The 16-gauge thickness offers a good balance of rigidity and workability — strong enough to resist bending and tearing under the duct’s load, yet not so heavy or stiff that it’s hard to form and install. Narrower or thinner strips (like 1 inch or 22-gauge) wouldn’t hold up well on ducts over 18 inches, while wider or thicker options (such as 2 inches with 14-gauge or 3 inches with 18-gauge) add unnecessary weight and bulk. So the recommended choice is 1-1/2-inch wide strips of 16-gauge band iron.