brush tip
Refers to the tip or end of a brush, such as a paintbrush or makeup brush.
刷毛先に絵の具をつける。
I put paint on the tip of the brush.
刷毛先が細いので細かい線
Because the brush tip is fine, I can draw thin lines.
Compound of 刷毛 (hake, 'brush') and 先 (saki, 'tip').