The Schmidt 888 refill is the most commonly used refill in rollerball pens. The Schmidt 888 is so commonly used it is easier to list the pens that it will not fit than the pens that it will fit.
Odds are your rollerball pen will take a Schmidt 888 unless it is one of the following brands:
Schmidt 888 refills do not fit: Parker, Sheaffer, Waterman, Pelikan, Cross, Montblanc, Lamy and most Chinese rollerball pens.
Absolute German quality and precision, cutting edge refill technology and specialised ink chemistry make the SCHMIDT 888 the best and the most reliable rollerball pen refill in the world. The Schmidt 888 has a state of the art ceramic ball and state of the art ink chemistry that combine to produce the smoothest writing experience possible. With its advanced ink technology, this refill is will not dry out for a full year, yet the ink will dry on the page almost immediately. This makes it ideal for cap-less rollerball pens and pens with caps that do not seal well.