Description This TWSBI stainless steel Medium replacement nib was designed for the TWSBI Diamond 580 fountain pen, so that you can change different nibs to suit your mood. Just unscrew the section, push out the old nib unit and insert the new one. These replacement nibs will fit the TWSBI Diamond 580, TWSBI Diamond 580AL and TWSBI Diamond 580ALR fountain pens. We offer Free Shipping on all orders over $59 for US customers, and for orders over $250 for our Canadian customers.