what is this foot for????
 

I found this on a search for a walking foot and now see they are everywhere for sale, but no listings tell me what they're for. I've googled it to death! The ridges are on the inside, so I can't see that it would be used like a walking foot to grip fabric..curiosity is killing me !

https://www.ebay.com/itm/Sewing-Mach...-/282409659673

Maybe you could message the seller and ask?

https://www.ebay.com/itm/Nylon-Ring-...-/401113137703
Here's a listing for a similar one. Scroll down for the description of what it does.

It's a fancy Teflon foot for sewing leather and vinyl

It is an embroidery foot. It will make a circle of whichever design you choose from the built in stitches or from a out source like a stick or computer download. I am guessing. Google circle crafts.

Interesting. I've never seen one before but my guess is that it would open up a seam while you "top stitch" from the underside. Or echo stitch next to a seam? This listing has a description.
https://www.ebay.com/itm/Industrial-Sewing-Machine-Parts-Presser-Foot-Double-Rolling-Ring-Presser/172594350769?_trkparms=aid%3D222007%26algo%3DSIM.M BE%26ao%3D2%26asc%3D20160323102634%26meid%3D02db0f a0353e4d2f8531bd960756d0a8%26pid%3D100623%26rk%3D2 %26rkt%3D6%26sd%3D282409659673%26itm%3D17259435076 9%26pg%3D2047675&_trksid=p2047675.c100623.m-1

It is indeed for leather work. I could not find a tutorial on how to use it but this may give you an idea.

https://www.aliexpress.com/item/3262...17e96c2c184b16

"This foot is great for sewing plastic, foam, polyethene, rubber backed and other materials not sewable with regular or teflon presser feet. Ring rotates as material passes under foot. Action eliminates friction. This foot prevents plastics, coated materials, leathers, etc. from sticking to foot. Allows for smooth sewing on difficult fabrics."

Thanks everyone. I still don't get it, though! I have never had leather "stick" to the foot. I don't get what this does that a standard roller foot.walking foot or teflon foot would do. Maybe it's just me, but I don't see a logical use for it!!

Looks really neat! Might come in really handy with some of the bag making I plan on doing.