I find that there is no sence to purchase a ball, or ball mount that is not strong enough to meet or excede the trailer rating. When out shopping for a trailer ball or a ball mount look for the highest rating you can get.
I have seen 2" balls with 7500lb ratings and 2 5/16" with 10,000lb ratings.
There are few companies that I have found that make ball mounts strong enough. Reese makes a solid ball mount rated at 10,000 lbs. Its heavy and can cost as much as $50 depending on where you get it.
1976 Soveriegn 31'
F250 Turbo 7.3L Diesel
WBCCI # 3516