See Figure 1
Figure the hitch weight to select a proper hitch. Hitch weight is usually 9-11% of the trailer gross weight and should be measured with the trailer loaded. Hitches fall into various categories: those that mount on the frame and rear bumper, the bolt-on or weld-on distribution type used for larger trailers. Axle mounted or clamp-on bumper hitches should never be used.
Check the gross weight rating of your trailer. Tongue weight is usually figured as 10% of gross trailer weight. Therefore, a trailer with a maximum gross weight of 2,000 lbs. (907 kg) will have a maximum tongue weight of 200 lbs. (91 kg) Class I trailers fall into this category. Class II trailers are those with a gross weight rating of 2,000-3,000 lbs. (907-1,361 kg), while Class III trailers fall into the 3,500-6,000 lb. (1,588-2,722 kg) category. Class IV trailers are those over 6,000 lbs. (2,722 kg) and are for use with fifth wheel trucks only.
When you've determined the hitch that you'll need, follow the manufacturer's installation instructions, exactly, especially when it comes to fastener torques. The hitch will subjected to a lot of stress and good hitches come with hardened bolts. Never substitute an inferior bolt for a hardened bolt.