See Figure 1
Calculate the hitch weight in order to select a proper hitch. The weight of the hitch 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 type, or the 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 2000 lbs. will have a maximum tongue weight of 200 lbs. Class I trailers fall into this category. Class II trailers are those with a gross weight rating of 2000-3000 lbs., while Class III trailers fall into the 3500-6000 lbs. category. Class IV trailers are those over 6000 lbs. 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 be subjected to a lot of stress and good hitches come with hardened bolts. NEVER substitute an inferior bolt for a hardened bolt.