What exactly is a "weight distributing hitch"?

[BillaVista]

I see a class III/IV trailer hitch advertised locally -

"rated 5000lbs gross trailerweight, 10,000 lbs with weight distributing hitch, fits most fullsize pickups" It looks like a standard looking 2" square receiver hitch.

So what is this "weight distributing hitch"? Is it for the truck or the trailer? Of course, there's no mentin of itin the catologue.

Thanks

[Tusker]

A weight distributing hitch fits on the tongue of the trailer and allows the connection between your trailer and tow vehicle to resist bending. They are the 36-inch or so long j-arms of spring steel running along the trailer tongue and attaching to two round receiver tubes beside the towing ball. A standard ball-to-hitch connection operates like a simple hinge and cannot transmit bending (like the pinned connections in a truss). As a result, the ball and hitch mount can only transmit vertical forces. This means the stress, strain, and vertical oscillations of your hitch are at a maximum. The weight distributing hitch forms a bridge across this otherwise flexible connection and allows the hitch to transmit bending forces between the trailer and tow vehicle. By utilizing both bending and shear at the hitch to carry the tongue weight, the stress, strain, and vertical movement on your trailer tongue and hitch are reduced and the same hitch setup can therefore carry more load.

[BillaVista]

Thanks Tusker, great description:

Here's a pic I found:

http://www.hitch-web.com/wd.asp

[Tusker]

That is it alright . They work great. If you get one, be sure not to overtighten the chains though. You want to balance the load equally between the ball and the weight-distributing bars. I've seen guys crank the bars up too tight and have the rear of the tow vehicle get real squirrely on them.