A Pittsburgh lock is a true lock because it has a 1/4" tail.

• A. Not sure
• B. Sometimes
• C. Yes
• D. No

Answer: (C)

The idea being tested is how a seam is considered a true lock in sheet metal work. A Pittsburgh lock earns the label true lock because its design includes a tail that interlocks with the adjoining edge. That 1/4" tail acts as the locking feature: when the seam is formed, the tail is tucked into the opposing leg and pressed to lock it in place, creating a solid, sealed joint that resists pulling apart. Without that tail, the seam wouldn’t have the interlocking mechanism that defines a true lock, so the statement is true.