Input: blue crank to which is fixed a yellow small worm (1 start, lead: t1, pitch diameter: D1).
Output: large worm (2 starts, lead: t2 = 2.t1, pitch diameter: D2 = 2.D1)
The output and the input rotate with the same velocity and direction.
The small worm can be replaced with a cylinder of circular grooves or with a rack.
If the yellow worm has revolution joint with the crank and there is sufficient friction between the worms, the output and the input rotate with the same velocity and direction too (the yellow worm doesn’t rotate on its pivot).
If not, the output rotates slower than the input.
Worm diameters do not play essential role in terms of kinematics.