Brush pens offer you a lot more variation in line width than the usual fineliner pen. Their nibs have a wide base that then tapers into a great stage. Usually the nib is fabricated from a conical bit of felt, but there are pens that have a true brush https://inkdrawingforbeginners32108.shotblogs.com/the-best-side-of-ink-drawing-for-beginners-49117481