<P> The cases of Zippo lighters are typically made of brass and are rectangular with a hinged top . On most models, the top of the case is slightly curved . </P> <P> Inside the case are the works of the lighter . The insert contains the spring - toggle lever that keeps the top closed, the wick, windscreen chimney, flintwheel, and flint, all of which are mounted on an open - bottom metal box that is slightly smaller than the bottom of the outer case, and into which it slips snugly . </P> <P> The hollow part of the interior box encloses five rayon balls (similar to cotton balls) which are in contact with the wick . The bottom of this is covered by a piece of felt approximately 1 / 4 of an inch thick . Printed on the bottom of the felt (in modern Zippos, not on older models) are the words, "LIFT TO FILL," to indicate one must lift the felt away from the "cotton" in order to refuel it . The fuel, light petroleum distillate or synthetic isoparaffinic hydrocarbon (commonly referred to as lighter fluid or naphtha), is poured into the rayon balls (sometimes called the "cotton," or the "batting"), which absorbs it . It also contains a tube that holds a short, cylindrical flint . The tube has an interior spring and exterior cap - screw that keeps the flint in constant contact with the exterior flint - wheel . Spinning this rough - surfaced wheel against flint results in a spark that ignites the fluid in the wick . </P> <P> All parts of the lighter are replaceable . The Zippo lighter requires 108 manufacturing operations . </P>

What is the screw for on a zippo lighter