Hitch (receiver) class
Receiver hitches are grouped into SAE J684 classes by maximum trailer weight: Class I up to 2,000 lb, Class II up to 3,500 lb, Class III up to 8,000 lb, Class IV up to 10,000 lb and Class V above 10,000 lb.
How this site uses it
The site derives the hitch class from each configuration's maximum trailer weight. The class tells you the receiver you need; it never raises the vehicle's own rating.
Related: Weight-distribution hitch · Towing calculator