Machinist's Screw Jack

[ProjectsInMetal]

I understand the principle of RH and LH threads working together to extend the jack, but I can't figure out how you prevent the internal set of threads from turning with the external threads. Is there a spline or keyway inside that we can't see that prevents one set of threads from rotating along with the other?

[elcaminos]

There is a spring inside connected at the top and bottom.

[ww321]

cool jack ! ! I like making stuff to check out my site. ..................J.W.