What is the key aspect for bottom side rail outward deformation measurement?

The measurement of bottom side rail outward deformation is critical for assessing the structural integrity and usability of a dry van trailer. The correct answer emphasizes that this deformation should not exceed the corner fitting side surfaces. This is important because if the deformation goes beyond the corner fittings, it may indicate structural issues that could compromise the integrity and safety of the trailer.

Maintaining the deformation within the limits dictated by the corner fittings ensures that the structural design of the trailer is preserved and that it can continue to perform as intended without risking failure during load handling. Deformations beyond that threshold could lead to improper loading, unstable handling characteristics, or potential failure in performance under stress.

The other options, while they pertain to measurements and deformation relevance, do not directly address the critical boundary set by the corner fittings, which serves as a standard for acceptable deformation limits in this context. Understanding this parameter helps ensure compliance with industry standards and safe operation of the equipment.