DIESEL Keeper ASD A Series 2 Anti-Siphon Device that fits on the diesel tank inlet of most Heavy Duty SCANIA trucks, Massey Fergusson and certain John Deere machines where the gas cap screws into a tank inlet approximately 2.625" ID and with at least 4.5" depth to allow for the fitting of the ASD. Comes with a standard Diesel Cap that fits onto the unit. The top grid is recessed approximately 1.5" and has a honeycomb shape. The bottom grid has a similar but smaller honeycomb design. The top flange is about 1.25" wide and has twelve openings on the inside grouped in six sections of two openings each around the circumference of the filler neck extension. These opening are to allow for air to escape as the tank is filled. At the bottom of the device there are six flow slots on the outer and inner sleeve, and further up the bottom part of the unit are six more flow slots on the outer sleeve only. At the bottom of the top flange is an aluminum thread with nine slots cut vertically into the groove - these gooves are grouped in three groups of three. Insde the upper flange are three pins that are hammered into the device once it has been tighted onto the diesel tank inlet. The Device comes with a built in filler neck extension. The diameter of the upper flange is 4.25" and the device is about 5.625" tall when measured from the bottom flow grid to the top of the flange. The filler neck extension rests at 4.125" tall when measured from the top honeycomb grid. The Device is designed to fit directly where the gas cap goes prior to installation. It causes the cap to be approximately 1.5" further away from the diesel tank once the ASD is installed. Be sure to check for adequate clearance prior to installation. A new cap comes with this device and is attached by way of a cable to the device. Any diesel screen below the diesel cap would need to be removed to allow for fitting and installation of the unit.