A trailer jack is a vertical device that allows you to lift or lower your trailer to ensure that it's perfectly level. The jack is positioned on the tongue of the trailer and is also used to hitch and unhitch your trailer from your truck or SUV. In short, if you have a travel trailer, you'll need a trailer jack. However, not all trailer tongue jacks are made equal. Different jacks have different lifting capacities and not all types are the same. Let's take a closer look.