Sensa rollerball pens will only take our Schmidt 8126 option (our Item R4611). Please choose carefully as customers often confuse this 8126 option with the P8126, which is much shorter. Montegrappa also offers a rollerball refill which will fit in your Sensa rollerball pen. With either option, it is always best to confirm the shape and attributes of your old refill with those of the refill you are purchasing. The length of the correct replacement refill should be 4-1/4".