In Marcus Ruthenberg's glass-ball sprinkler, what holds the lever arrangement in place?

• A. A steel pin
• B. A fusible solder
• C. A riveted bolt
• D. A rubber gasket

Answer: (B)

The lever is held in place by a fusible solder. In this glass-ball sprinkler, a small solder link acts as a temperature-sensitive fastener that keeps the lever secured until the surrounding heat reaches its rated point. When the solder melts, the lever is released, the glass bulb is affected by the heat, and the sprinkler can operate. The glass ball itself is the visible temperature-sensitive element, but the actual retention mechanism is the fusible solder, designed to fail at a specific temperature. Other mechanical options like a steel pin or riveted bolt would not provide the required predictable release at the designated heat, and a rubber gasket wouldn’t give a reliable, heat-triggered release.