What is the diameter of a sheave measured at?

The diameter of a sheave is conventionally measured at the center groove of the wheel. This is the part of the sheave that directly interacts with the rope or cable that runs over it. By measuring the diameter at the center groove, it ensures that the crucial point of contact between the sheave and the rope is accurately accounted for.

Understanding this measurement is important because it affects how the rope fits and performs during rigging or rescue operations. If the diameter were measured from other parts of the sheave, such as the outer edge or the flat surface, it would not provide an accurate representation of how the rope would engage with the sheave, which could impact load distribution and the efficiency of the system used in rescue scenarios.