Artdone Metallic Nail Art Pens, Liner Brushes Set, 5PCS Black Color Nail Tools For Long Lines, Thin Details, Fine Drawing, Liner Brush UV Gel Polish Painting Nail Design Sizes 5/8/12/20/25mm

The specific brushes I use are from a local nail supply store and they have been the only brushes I've seen that are thin enough for the details I want. However, before I found these magical brushes, I used basic nail art brushes that came in a multipack from amazon, and cut them hair by hair till I got the thin brush I needed. Time consuming but worth it if you cant find anything else. But investing in nice long striping brushes help a lot we straight lines. I use these for frenchies/color blocking/stripes: Nail Art Brushes