Abstract: An improved trailer jack has a castor structure enabling use of a full size spare trailer wheel and tire on the jack; the jack has a gear box mechanism, a lift post drivable up and down by the gearbox, and a lift element pivotally journaled inside the post; the lift element has an offset structure which raises the spare axle axis up to a level above the bottom of the post and the axle is spaced to one side so that when the full size spare wheel and tire is used, it pulls up into a locked storage position above and alongside on the trailer tongue, when the spare is down, it swivels completely around under the tongue and around the lift post. The trailer is much easier to manually manipulate in a garage or driveway.An improved lift assembly with a unique swiveling lift member having both a trailing offset and transverse offset is utilized.