A capillary nib for pens is shaped from a thermoplastic resin bar and has a cross-sectional shape comprising an outer shell and a plurality of projections joined integrally at their bases to the outer shell at equal angular spacing intervals and projecting centripetally toward the center of the cross section, voids constituting principal capillary ink passages being formed between the projections, alternate projections extending fully to the center and being joined together. The thermoplastic resin bar is formed by extruding the resin in molten state though a die having a large number of orifices disposed in a specific arrangement thereby to form a plurality of filaments of the resin and causing the filaments to adhere longitudinally while the surfaces thereof are still substantially in molten state thereby to form the bar. Each passage or channel has substantially identical transverse width across its cross-sectional area.