Input: small worm, 1 start, lead: t1, pitch diameter: D1
Output: large worm, 2 starts, lead: t2 = 2.t1, pitch diameter: D2 = 2.D1. It has prizmatic joint with the base.
The output moves t1 in 1 rev. of the input.
The output can be of circular grooves in stead of thread.
The large worm can be replaced with a rack (like in adjustable spanners).
If the large worm has cylindical joint with the base, the output motions (linear and rotary) are unstable.