I have one of those tripod jacks. They were marketed in the 50's as a safer alternative to the bumper jack.
http://blog.modernmechanix.com/tripod-jack-for-cars-is-advertised/
X3 or is it X4 on Harbor Freight.
Buy a new one and get the warranty, used is a crap shoot unless you are already an experienced welder and you can test it out before buying.