Ballpoint pens have a tiny ball made of brass, steel, or tungsten carbide as their writing tip. A compartment called the ink reservoir holds the ink, and a narrow tube links the reservoir to the ball. The ball, which is fitted into a socket, turns as it rolls across the paper, carrying ink from inside the pen onto the paper. Many ballpoint pens have a plastic cap that helps prevent ink from drying out on the ball. On others, a push-button mechanism draws the pen point into the body of the pen. Most ballpoint pens depend on gravity to pull the ink to the ball. For this reason, ballpoint pens generally do not write well when held sideways. However, some ballpoints are designed so that slight pressure is always applied behind the ink column. This design enables the ink to move constantly forward and the pen to write even when its point is higher than its back end. Ballpoint pens use a thick, sticky ink because a thinner ink would leak out around the ball. But the use of such ink makes ballpoint pens write less smoothly than most other pens. 2000pcs/ctn