Hagan Street Rod Necessities gas caps fit Hagan fuel doors and are made to screw into late model large thread filler spouts. They are vented caps and are also available in a 'fill-through" design so you never have to remove the cap to re-fuel, just push the pump nozzle through the center valve. Fill-through caps are vented for vacuum and can be modified to vent for pressure.
Note: California users or others using vapor recovery fueling systems please refer to the McCuff Sport at McCuff.com to prevent damage to the cap.