What is the name for wood members graded according to the load carried on their cross-section?

The term used for wood members graded according to the load they can carry on their cross-section is "posts and timbers." These members are typically larger dimensions of lumber that are specifically rated to support vertical loads and are fundamental in structural applications.

Posts are vertical members that carry loads from the structure above, while timbers can serve various structural roles and are used to create frameworks or supports for buildings. The grading of these members is essential for ensuring that they are capable of supporting the intended loads and meeting building codes.

The other options listed refer to different types of wood members or components used in construction but do not pertain to the grading system based on load-carrying capacity in the same way that posts and timbers do. Thus, understanding the specific context and applications of each option helps clarify why "posts and timbers" is the appropriate choice.