What is the longest hitch extension for a factory class IV receiver?

I heard it was 18".....I wanted to see what everyone else thought or knew.

Thanks

 

You can use as long as an extension as you want, however the longer it is the less weight you can put on it. I used an 18" extension with my stock hitch and a 7000# car hauler. I could see the stock hitch flex as I put the trailer weight onto the ball.

I replaced the stock hitch with a heavy duty Putnam receiver. No more flexing of the hitch but my first trip out with the receiver extension and new hitch the extension bent down.

No more extensions with a 2" receiver for me. Not sure how heavy you are towing but unless its a light utility trailer I wouldn't bother trying to use an extension with any 2" receiver.