The rolling ball is so small that the line it leaves is perfectly acceptable to form letters from, but not so small that it cuts through the paper. It is machined accurately so that it almost fits into its holder, but with enough gap to allow the ink to pass over it when pressure is applied. However, it doesnŐt wobble about and so accurate lines can be drawn. The ink is of ideal consistency, flowing easily but not so liquid that it will splatter past the ball if the biro is shaken.
The nib assembly slots neatly into a plastic tube that is hexagonal on the outside to facilitate grip and circular inside to allow easy insertion of the inner. The outer also has an airhole to ensure that the ink flows easily and is not restrained by a vacuum. There is a small top to prevent it snagging on anything and is colour-coded so that the ink colour is easily identifiable. A cap serves both to prevent the ink around the ball drying out and also serves as a clip to allow the pen to be worn in a pocket. And all manufactured, marketed and distributed for a few pence!