I bought this new foot for my machine because I had read about it on the craftsy site that offers classes and I was reading about the knits class. I didn't sign up for the class. But it looks interesting.
It's a Roller Foot. Has a large roller on one end and two little ones in the back.
Below are photos for your viewing pleasure.
The first shows the bottom. This is whet will go against the fabric. And the size.