The Crown Brush Backstage S217 Round Contour Brush is ideal for defining the outer v. It is soft, dense and stiff. You can also use this brush to blend, but I find it to be a little small. I would use this brush mainly for contouring and adding color to the outer corner.
The handle of the brush says "S217 Round Contour." The head of the brush is 1 centimeter long. The total length of the brush is 5.5 inches. It is small enough for travel. I bought this at CrownBrush.com for $1.87.