What is the term for one of the two main structural components that run the entire length of most ladders or ladder sections?

The term for one of the two main structural components that run the entire length of most ladders or ladder sections is referred to as a beam. In ladder construction, beams are the primary vertical or longitudinal elements that provide structural integrity and support. They are essential because they help distribute the load and maintain the ladder's shape and stability when in use.

While the other terms mentioned have specific functions in ladder design, they do not represent the main structural components in the same way. "Fly" refers to the part of an extension ladder that can be raised or lowered, whereas "rung" identifies the horizontal steps that provide footholds for the user. A "cross member" is typically used to connect two beams or elements but is not one of the primary components running the entire length of a ladder. Understanding these distinctions is crucial for recognizing the parts of a ladder and their respective roles in safety and functionality.