Stretched One-Piece Fat Bob Gas Tank for Harley Sportsters Custom One-Piece Stretched Smooth-Top Gas Tank Tank for Harley-Davidson Sportster XL Models For models from 1982 to present and any Custom Application 4 gallon (15 liter) capacity. (Almost twice as much as the original tank) No longer is trick paint enough to define a hot custom. But add a custom tank and the crowds will pause longer to look at a tricked out bike. New stampings rather than using welded tips to achieve stretch. Dual cap tank.