They say you shouldn't jack your rig up by placing a jack under the axle. Axles are to cheap/thin walled, and you might collapse them.
I carry one of these with me.
I also have a 20 ton bottle jack. I welded a 3 or 4 in. piece of angle iron on a short pipe. It sits on top of the jack and cradles the axle. I use this at home when I'm changing tires, doing the wheel bearings, and adjusting brakes.
I haven't had to use the trailer aid-------------yet.
I also carry a breaker bar with appropriate sized socket, and a torque wrench. I torque to 85#.
Edited by: Old Farmer