1.Fitment: Transfer tank vented cap replace for Dee Zee FillRite transfer tank cap and fit for standard 2' NPT threaded tank bung base. Diesel tank cap works well for ground, farm, commercial and distillate tanks, such as transfer tank, fuel tank, gas tank, diesel tank, auxiliary fuel tank, mobile fuel tank and weather guard tank. 2.Both Directions Vent: When loosing the diesel tank cap, the venting pressure tank cap vents pressure inside the fuel tank to outside and releases dangerous vapor build up to prevent overexpansion of the diesel fuel tank. And vented fuel cap allows air into the diesel transfer tank to prevent vacuum forming and collapse the tank when you draw out fuel. 3.Added Security for Diesel Tanks Fuel: Lockable diesel fuel tank cap fits for 1/4' 5/16' diameter shackle padlock (not included), which secures your fuel tanks and prevents costly oil fuel from theft, tampering, siphoning and vandalism. Just put a padlock in lock hole that is right on one of the tabs on the base and the tabs will hold the lock. 4.Prevent Leaking: Transfer tank fuel cap with spring loading and inside gasket seals when tightly closing to prevent leaking and excess gas vapor venting even when driving on the road. 5.: Align the vented gas cap with the notch, push down and clockwise twisting to tighten the diesel tank cap all the way. To remove transfer tank cap, counterclockwise twist slowly to the notch to vent pressure. Push down and twist to lift pressure vent fuel cap and remove.