One of these also works well.
But I also carry a bottle jack. As for weight rating, You figure you are only lifting 1/2 the weight of the trailer. So, depending on your trailer, a 2 or 3 ton jack would work. Bottle jacks are cheap though. I think I have a 5 ton for my 8000 lb 5er.
One other thing to consider is axle height... when the tire is flat. My bottle jack is just tall enough to sit on a 2X8 board and fit under the axle with the flat. I think going with a 10 or 12 ton jack may be too tall.
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