Your hitch system is only as strong as its lowest-rated component. To find your hitch system rating, compare ratings of your hitch, hitch ball and ball mount as shown below. Your hitch system rating is the lowest rating among those parts.
Your hitch's maximum tow weight rating can usually be found on a label on the hitch itself.
Hitch ball rating
Your can find your hitch ball rating on the top of the ball, or around the base of the shank.
Ball mount rating
The rating for your ball mount is usually on a label on the mounting plate or along the shaft that goes into your receiver.
Hitch system rating video
This video also explains how to find your hitch system rating.