What is the indicator notch on hose couplings that lines up when the threads are aligned for proper engagement?

The Higbee notch is an important feature on hose couplings that serves as a visual indicator for proper engagement. It is designed to align with a corresponding notch on another coupling when the threads are properly lined up. This alignment is crucial for ensuring that the coupling can be easily threaded together without damaging the threads or compromising the seal.

The design of the Higbee notch allows firefighters and personnel to quickly identify when the couplings can be safely engaged, which is vital during emergency situations when speed and efficiency are imperative. This feature helps prevent cross-threading, making the process of connecting hoses safer and more reliable. In contrast, the other terms mentioned do not specifically refer to this particular design feature in hose couplings, focusing instead on different aspects of hose coupling operation or nomenclature that do not provide the same level of clarity or precision.