Rollover fuel protection: Rubber flapper valve automatically seals the filler opening if the vehicle becomes inverted to help prevent fuel leakage Sanctioning body approved: IMCA-approved safety component and required by most oval track and short-track racing organizations Fueling functionality: Flapper opens during normal fueling and closes instantly in rollover situations for reliable spill control Complete mounting hardware: Includes nylon sealing washers, nylock nuts, and 1/4-inch retaining studs for secure installation Fuel cell compatibility: Designed to install between the filler cap flange and fuel cell using standard bolt patterns found on Jaz-style fuel cells This flapper valve or rollover valve, installs in the fuel cell and is retained by the bolts used to secure the filler cap flange to the cell. When fueling the cell, the rubber flap opens. If the cell should become inverted, the rubber flap closes to seal off the filler opening so that fuel cannot leak out. A must have safety item! IMCA approved. Value added kits are now available which includes both the cap and neck as kit # 916-02008 and a rollover flapper valve kit # 916-02007