A ballpoint pen (Hungarian: golyóstoll, also eponymously known in British English as a biro an pronounced /ˈbaɪroʊ/ bye-roe in Britain but sometimes /ˈbiːroʊ/ bee-roh" elsewhere, named after its inventor László Bíró), is a modern writing instrument. A ballpoint pen has an internal chamber filled with a viscous ink that is dispensed at the tip during use by the rolling action of a small metal sphere (0.7 mm to 1.2 mm in diameter) of brass, steel or tungsten carbide. The ink dries almost immediately after contact with paper. Inexpensive, reliable and maintenance-free, the ballpoint has replaced the fountain pen as the most popular tool for everyday writing.