SCHMIDT P950 ballpoint refill air pressure Medium

Schmidt Megaline P950M pressurised refill in G2 ‘Parker-style’ format – converts a huge range of pens into ‘space pens’. The air pressure technology allows this refill to write upside down, in zero-gravity, in extreme high or low temperatures and on difficult surfaces – it also gives virtually unlimited shelf life. 
Also Schmidt P950 Ball Point Refill Fits:

Ancora, Aurora, Bexley, Bossert & Erhard, Caran d’ Ache, Cartier, 
Colibri, Delta, Dunhll, Elysee, Jean-Pierre Lepine, Lamy, Lanier, Lodis,
Monte-Verde, Marlin, Michel Perchin, Montblanc, Montegrappa, 
Northpointe/Libelle, Omas, Parker, Pelikan, Retro 51, Rotring.