Wolf the ball size is either 2" or 2-5/16 " most likely it is 2" make sure you get a ball with correct stem size 1' or 1-1/4" that fits your receiver. Also make sure your receiver mount on your vehicle is rated for the weight of the trailer.

You need to have the right size ball or otherwise it will come off when you hit a bump.  Most trailers list the ball size on the hitch.  If it does not say i have a 2 inch ball you can try.  

Bill

What size is the travel trailer? Most travel trailers are 2 5/16. Also make sure the ball mount is strong enough to support the trailer. Also if it is an older trailer it is probably pretty heavy and the brakes probably dont work, so give youself plenty of time to stop.

Be sure and use a decent sized safety chain as well.  My sister has been towing horse trailors for a 1/4 century without incident but last May the bulldog hitch failed where it hinges and her chains were way under sized.  The result was one dead horse one and one horse with broken jaw.  

Go to a scale and have the trailer weighed.  Hitch balls do have weight ratings, so be safe. Make sure your hitch is rated well too.  Having an accurate weight will insure you are not overloading your tow vehicle.  Be sure the hitch ball is torqued properly, preferably with a long pipe wrench, and then a couple tack welds on the nut to be safe.  I had a friend lose a trailer because the ball wasn't tight.  I have had a couple loosen up on me too.  

A good sway control is very cheap, usually around $100.  It will keep you safe in cross winds, a good investment even for the lightest trailers.

Depending on what you tow with, you may consider a load distributing hitch.  It will keep your vehicle level, help the steering and steering geometry, and keep the brakes on an even keel.

I tow 10000 pounds, so all of this was mandatory for me.

Dual safety chains are best, and should be crossed into and X, right to left, left to right.  The safety chain rating is important, so is the attachment points, as well as the hardware you use to attach the chains......only as strong as the weakest link.

Definately spend time on these things now, and you won't have to give it another thought down the road.

Look at them tires too.  If they have dry rot, and/or are around 7+ years old, guess what will happen at freeway speeds on a hot day?  Yeah, I overlooked this one.  Glad I had a spare and a jack.

Quoted: Quoted: Wolf the ball size is either 2" or 2-5/16 " most likely it is 2" make sure you get a ball with correct stem size 1' or 1-1/4" that fits your receiver. Also make sure your receiver mount on your vehicle is rated for the weight of the trailer. Thanks, I've got a 2004 F-150 with the trailer package and this trailer I'm towing is small so that isn't a problem. Will a 2" ball be sloppy if it requires a 2 5/16"? On the other hand will a 2 5/16" not fit at all if it requires a 2" ball? Should I just buy both and see which fits?

Wolf your factory hitch will be fine and as others have said you can't use a 2" ball on the 2-5/16 because it will come off. You could get a converta ball that has all three sizes of ball but it is rather expensive. Your tongue hitch should be stamped with the ball size so that you get the correct one.