Brush pens give much more variation in line width than the usual fineliner pen. Their nibs have a large foundation that then tapers to your fine place. Ordinarily the nib is made from a conical piece of felt, but you will find pens that have a true brush idea https://inkpendrawingtechniques26047.theobloggers.com/41467514/not-known-factual-statements-about-ink-drawing-for-beginners