What are duo fiber brushes used for

Ultra-Fine Eyeliner Brush for Makeup - Soft, High-Quality Fiber Bristles, Easy To Use, Black Wooden Handle, Brow Makeup Brush (E835)

Dual-Use Nail Brush Pen Fiber Bristles Metal Body Multifunctional Nail Pen for Sculpting And UV Nail Art

4/8/12pcs Cute Cartoon Cat Ultrafine Fiber Sponge Brush Multipurpose Cleaning Tool for Kitchen,Bathroom and Furniture Gentle On Surfaces,Easy To Use

Dual-Use Nail Nail Pen Metal Fiber Bristles Brush Body Multifunctional Pen for Sculpting And UV

Yousheng Dual-Use Nail Brush Pen Fiber Bristles Metal Body Multifunctional Nail Pen for Sculpting And UV Nail Art

Standard Series, Duo Fiber Tapered Blending Brush, Eyes 787, 1 Brush

Dual-Use Nail Brush Pen Fiber Bristles Metal Body Multifunctional Nail Pen for Sculpting And UV Nail Art