Every manufactured chain and strap has a working load limit (WLL) that is approximately one-third of its break strength. When manufactured, all chains are marked with a grade rating. This rating, which may differ by manufacturer, corresponds to the WLL of the chain. If the rating is not visible, assume that the grade is 30, the lowest grade. It is recommended that the total WLL of all tie-downs must equal at least half of the cargo's weight. For example, if you are hauling a small tractor that weighs 12,000 lb., you will need at least four tie-downs with a combined WLL of 6,000 lb.
Periodically inspect chains for deeply nicked or cracked links. Remember, "a chain is only as strong as its weakest link." Additionally, remember that the chain hook must have a closure to prevent the hook from slipping off the chain during use.
For more information, click here to be directed to the U.S. Department of Transportation, Federal Motor Carrier Safety Administration.