Uni-Ball AIR Micro - 0.5mm Fine Rollerball - Pack of 3 - Black, Blue, and Red - UBA-188-M The revolutionary nib of the Air, unlike conventional rollerballs, is pressure sensitive, meaning that it gives a writing experience and differentiating line width similar to that of a fountain pen. The metal ball of the nib is encased in an acetal plastic, rather than the standard metal surround, which allows for a smoother flow of ink around the ball, and an increased flow as further pressure is applied. The 0.5mm ball delivers a line width of between 0.28mm and 0.45mm (dependent on pressure). Features Uni's high quality "Super Ink", which is not only water and light resistant, but also "Tamper-Resistant", meaning that the ink cannot be washed off using chemicals and solutions used by people to fraudulently modify documents. Pack contains one of each of the following coloured inked pens: Black, Blue, and Red.