What should be checked on the header board during a pre-trip inspection?

During a pre-trip inspection, checking the header board for holes or missing rivets is essential because these conditions can lead to structural integrity issues. The header board supports the load of the cargo and provides stability to the trailer. If there are holes or if rivets are missing, it could compromise the strength of the header board, making it susceptible to failure during transit. This could potentially lead to a loss of cargo or even an accident, therefore ensuring that the header board is intact plays a crucial role in safety and compliance.

While the other options include important aspects to review in a broader inspection context, they do not provide as immediate a safety concern relating to the mechanical integrity of the vehicle as checking for structural issues on the header board does.