Replacement nib unit for TWSBI Diamond 580 fountain pens. Includes both the nib and clear Diamond 580 grip section with a metal ring. Also compatible with Diamond 540 pens by swapping the old grip section. Features a polished steel nib engraved with the TWSBI logo and branding. Available in various nib sizes: fine, medium, broad, extra-fine, stub 1.1mm, and stub 1.5mm.