Pack of 4, Tombow 55691 O3p X-fine 0.3mm Black Rollerball Refills Pack of 4, Genuine Tombow O3P, 0.3mm x-fine, black ink rollerball refills Waterproof fast-drying ink. Tungsten carbide rolling ball for unequaled smoothness. Won't smear skip or fade. Fits all Tombow refillable rollerball pens.