The five-sided component on the top of a hydrant is the

• A. Cap
• B. Operating nut
• C. Stem
• D. Flange

Answer: (B)

The part you turn to open or close a hydrant is the operating nut. This five-sided knob on the very top is specifically designed to be gripped by a hydrant wrench, so you can apply torque to the valve inside. When you rotate the operating nut, it moves the stem, which raises or lowers the internal gate to control water flow. The pentagonal shape helps prevent slipping and gives a good grip with standard tools.

The cap is simply a protective cover for the outlets and isn’t used to operate the valve. The stem is the internal rod that actually translates the turning motion of the nut into vertical movement of the valve—it's inside the hydrant and connected to the gate. The flange is a mounting or connection ring, not the component used to operate the valve.