Smith Cosmetics 202 Microliner Brush is a brush that retails for $16.00.
Smith Cosmetics 202 Microliner Brush ($16.00) is an ultra-fine pointed liner brush. It's made out of synthetic sable bristles, and it's firm brush that flexes enough to line along the curve of the upper lash line but it moves together as one so there is no streaking or visible brush strokes. The brush has a total length of 6.00 inches / 15.50 centimeters, and the brush head was in 1.00mm width, 5.50mm length, and 1.00mm thickness (at its widest/longest points). If you work with a lot of gel and cream eyeliners, I could see this being very useful for precision work and very fine lines. If you tend to do thicker eyeliner, you'll likely want to opt for a thicker brush overall (you can layer and build out your liner with this one, it'll just be faster for a more appropriately-sized brush). What I found impressive was that it didn't feel sharp or pokey, even with the tip of the brush against the lash line, so you can really get between lashes, if desired.
Used for precise application of liner at the base of the lashes, this brush is made of soft synthetic sable with short bristles that give it the stability to be used straight or on its side.