Machinist Jack

[Toolmaker51]

...Agreed, never too many clamps. What I thought was ingenious about your machinist jack build was the ball bearing...Very cool! Interesting use and a good topic possibly for various uses of these versatile & handy little tools. ~PJ

Probably my oft-used case for machinist jacks is inspection. They'll support most any object which hasn't a flat or plane to start from on a surface plate, or machine table.
Usually I set two an arbitrary height [via height gauge] and regulate the level position with the third. Just takes an indicator to finish within small increments, but I start with the height gauge, subtracting highest reading from lowest. Also pays to record amount of change your jacks produce in one revolution, write it on the base. Since so many varieties exist, none are same thread pitch, it's the easiest reference.
IMHO, some commercial jacks have too-small a thread diameter + too-coarse thread pitch. Those detract from the purpose. That is avoided making your own, in mind a decent diameter and small pitch support more weight, while offering greater mechanical advantage by lessened pitch incline.
While satisfying to achieve a close fit, they work best if they turn easily! A wrench is convenient, but can be fiddly. I like small crossbars more, and just in case, 4 wrench flats, not 6.
Why you ask?. Because 4 flats have more engagement area in a smaller equivalent wrench size!