Fire Safety, Extinguishers, and Rescue Techniques Practice Test

In a trussed beam, the long members that run along the top and bottom edges form the main load-carrying path. These are called rails, the top rail and bottom rail, which together carry the bending loads by taking compression (top) and tension (bottom). This naming points to the function of those pieces as the primary boundary members of the truss, with smaller internal members (webs) connecting them.

Railing would imply a safety barrier rather than a structural member. End cap refers to a finishing piece at the end of a member. Support is a generic term that doesn’t specify the top/bottom boundary members of a truss. So the term that correctly identifies the top or bottom component of a trussed beam is rail.