The hitch ball is a small part of a complex engineering history of trailer coupling that is nearly 100 years old. Hitch balls come in a variety of sizes for a variety of jobs.

The tri-ball piece rotates on its own, so the hitch does not have to be removed to change size. The smallest 1 ⅞-inch ball is rated for 3,500 pounds, while the two-inch gets a standard 7,500 ...