Your S.T. Dupont multi-pen has ballpoint options that can be replaced with the Monteverde liquid ink mini ballpoint refill. This 2-5/8" long refill is offered in up to eleven different colors.
Some models of S.T. Dupont multi-pens utilized .5mm lead and some used .7mm lead. It will be necessary to know the correct size before ordering replacements. If you purchased the multi-pen from us, we may be able to tell you which size you needs since we can look up the model you bought. Just give us a call at 800.766.7367.