Metal pens were tried next, but many metals were not flexible enough. The writing styles which developed with quill pens used thick and thin strokes. People wanted the same flexibility from a metal pen. Between 1839 and 1849 the steel-nibbed pen solved the problem. For the next century and more, industrial production lines turned out hundreds of millions of steel nibs. They had the advantage that different types of nib could be attached to the same holder. This allowed for different styles of writing to be used. Eventually the best nibs were tipped with gold or iridium, a rare metal which arrives on Earth via meteorites. All stages in the making of nibs was done by machine. The great secret of all nibs from the Egyptian reed to the steel pen is the slit down the middle of the tip. This leads the ink from the small blob under the nib to the point where the ink goes onto the paper. Without the slit, a nib does not work well.