Chains must be marked with a grade that determines their:

The correct answer is pertaining to the working load limit of chains. The working load limit (WLL) is the maximum load that a chain is designed to safely handle during operation. This limit takes into consideration factors such as the material and design of the chain itself, ensuring that users can operate within safe parameters to prevent accidents or failures during lifting or securing loads.

Marking chains with their working load limit is crucial as it provides essential information that helps users avoid exceeding the safe operational capacity of the chain. This is particularly important in vehicle rescue scenarios where the safety of rescue personnel and the integrity of the vehicle being handled are paramount.

While resistance limit and breaking load are important concepts in understanding the capabilities of chains, they do not specifically represent the maximum weight the chain can lift safely during regular use. Additionally, durability rating usually refers to the longevity of materials under specific conditions rather than their operational load capacity. Therefore, the emphasis on the working load limit highlights its necessity for ensuring safe and effective use of lifting and securing equipment.