What term describes the narrowest portion of the threaded part or hole?

The term that describes the narrowest portion of a threaded part or hole is the minor diameter. In the context of screw threads, the minor diameter refers to the diameter measured across the bottom of the thread grooves. This measurement is crucial as it indicates the smallest diameter at which the thread can be engaged during the mating process with a corresponding threaded component.

In practical applications, knowing the minor diameter helps in assessing the fit and strength of threaded connections. It ensures that the screw or bolt can be correctly engaged with the nut or threaded hole, allowing for proper assembly and functionality of mechanical systems. Understanding this dimension is essential for engineers and machinists to ensure optimal performance and safety in mechanical designs.

Other terms such as major diameter and pitch diameter refer to different aspects of threaded geometry—major diameter being the largest diameter across the crests of the threads, and pitch diameter representing an effective diameter at which the width of the thread is equal to the space between threads. Thread depth, on the other hand, refers to how deep the thread grooves are cut into the material, rather than a specific diameter measurement. Understanding these distinctions helps clarify the significance of the minor diameter in threaded applications.