These flatside Fat Bob gas tanks have a 2 inch stretch to help fill the void between the tanks and the seat. With a 5.5 gallon capacity, they are just what you have been asking for. These utilize the OEM style 13/16 inch fuel petcock. Includes flush mount locking gas caps. Fits Softail 1984-later and Big TWin with split tanks 1985-later. We recommend fuel tank liner combo pack (#05419) for sealing.