Most often the towing capacity of a truck is determined by the weakest link. The ball, the coupler and the hitch many times have different ratings. 10,000, 6,000 with load distributing bars, 5,000 tongue weight. The truck frame is probably the strongest item in the mix so the rating will start with the hardware used to secure the receiver hitch or, in the case of Cujo8, the bumper to the frame. Grade 5 or Grade 8 minimum. If you are not sure of your hardware or what you have is old original bolts/nuts, change them out to a known quantity. You can get Grade 8 hardware from any good hardware store and Lowes has it also. (Home Depot has chosen not to carry it in the Houston area). The hitch pin that holds the hitch bar in the receiver is also another link that must be up to spec for your application.
I would rate the Bardon bumper as a 5,000 lb max. Always use safety chains and criss-cross them under the tongue of the trailer.
On my rig, the trailer is rated at 7,000 lbs but weighs in at 1300 so I can carry anything 5,700 lbs or lighter. Most cars and trucks are around 4,000 or less so I feel I am good with a 6,000 lbs rated ball. Others may want more of a margin. As long as you are on the high side then I feel you are safe.
