This is the set for the Janome 6500P (Singer S18, which is what I have)
[ATTACH=CONFIG]542313[/ATTACH]
The difference between it and the hopping foot is the bar that sticks out of the one I'm holding and fits over the needle bar of your machine. That's what makes it "hop".
[ATTACH=CONFIG]542314[/ATTACH]
And, here's how Leah Day makes her own....
http://leahday.com/pages/break-your-darning-foot
Watson