I got tired of laying my hand on the X axis, while working on the hotend, and the bar creeping down. At first I was using a piece of dowel rod, it kept slipping one way or the other. This jack is 6" high, with a good wide base, putting the hotend at the perfect level to see what you are doing, when changing nozzles, etc.

Should fit virtually any printer, at least all the most common budget printers.