This is a new kind of ring stretcher and works similarly to a rolling mill but on a smaller scale.
First thing to do is choose the fitting that best matches the back of the ring and fit it into the tooling. It is best to choose one that is not too tight round the shank.
Next mark on the ring with a marker pen where the shank gets larger as you want this to be where you stop stretching.
After placing the ring in, tighten up finger tight but not too tight.
Rotate left and right stopping at the pen marks, then tightening half a turn and rotating again, i did this 3 times and it made the ring fit a lot better.
The ring stretcher has its limits to about half a size but it is a good bit of kit for less than £20 and it required no cutting or soldering and i am so glad i bought it.
This is how i did it and is not a tutorial so proceed at ones own caution.