There comes a time in every artists' life that there is a need for something that doesn't exsist. When that happens you "improvise" with what you have on hand.
Such was the case when I was working on a Teddy Bear. I wanted something narrower than what I had, and what I knew was available. I took a Langnickle feather brush and cut down both sides leaving just the middle "hairs" for painting with. Now I find that I use this brush a lot for grasses, small work that I enjoy doing, Santa's beard, mustache, etc. I don't recommend using a brush bigger than 3/8" for the feather brush as the bristles are the longest in the middle. Too long and they won't be as "stable". This one works great for what I need.