This special Fisher Space Pen pressurized refill will fit all Fisher Space pens except the mulit-action pens, and can be converted to fit a Parker ball pen.The Fisher ball pen refill is pressurised with nitrogen, enabling it to write on most surfaces at any angle. This pen can even write under water and performs in extreme weather conditions. This ballpoint pen refill can be converted to fit pens that take the standard-sized Parker refill.