Which statement about coffin locks is correct?

• A. It is soldered.
• B. It is riveted.
• C. It is welded.
• D. It is glued.

Answer: (A)

Coffin locks are a type of sheet-metal corner seam designed to be sealed with a low-heat joint. The interlock creates a tight, box-like corner, and the seam is closed with solder to form a continuous, leak-tight surface without distorting the thin metal. Soldering is preferred here because it provides a strong, smooth joint on thin gauge material without the heat, warping, or discoloration that welding can cause. Riveting would add mechanical fasteners but wouldn’t seal the seam; gluing isn’t durable for metal joints. So, the statement that coffin locks are soldered best describes how they are joined.