I don't know but it makes a great machine applique stitch. I'm not using it like it's suppose to be used. I'll have to look up what couching is.

Couching is where you lay a heavy cord, ribbon, yarn etc on the top of the fabric and then zigzag over it. A couching foot has a channel to allow the embellishment being applied to run under the foot.

This is what my couching foot looks like.

http://www.sew4less.com/product/4808...for_model_info

interesting question - I didn't know either, (p.s. I love that company, super fast ship)

That is an interesting foot! i'm wondering if the decorative material you are couching goes under that little clip. If it is a little clip... :-0
here's a definition of "Couching"
Couching is derived from the French word couchier and is the art of embroidering by laying threads flat on a surface and sewing them down by stitches sewn at regular intervals.

In centuries past, couching was a very popular form of decoration for the upper-class clothing of the time. People of means would often wear items which were covered in couched and embroidered designs.

The couching of today is generally done by laying a length of yarn, cord, or ribbon down on a piece of fabric, and then sewing it in place with a zigzag or other decorative stitch. Today, couching is used to sew on many of the more decorative fibers and trims available to those who sew at their local craft stores.

I haven't noticed a channel on the foot but there is a metal band going across it that lays very flat against the foot. How to use it is not in my manual.
Here is a close up of the stitch I used to applique. The blue is appliqued to the yellow. I used yellow thread to try it out but I can tell if I used blue it would be almost invisible. It's a super close up picture.

My machine is computerized and the screen says this is the couching stitch and shows me what foot to use. I can adjust the V stitch to teeny tiny or to take a bigger bite. I need to use all the attachments that came with the machine, I might learn something new. The picture is just with the foot and plain sewing no extra cord or thread being feed through the foot.
Wow, it just hit me I could attach a thin cording to the edge of the applique. How cool is that?

My couching foot for my Janome is much smaller than the one you pictured.

I'm sure this is out of date, but couching when I did it years ago was feed dawgs lowered for free motion and I would have a piece of yarn or ribbon and would position under the needle to sew over for making designs etc. before all the new models came out.

I use my couching or my cording foot to attach those funky crazy yarns that are available now to fleece Linus quilts. You can also decorate the necklines, pockets, sleeves etc. on clothing. It is amazing what a few lines of colorful, colorfast yarn can do for a plain T shirt. Have fun.