When working on Common Rail Diesel fuel systems it is essential to avoid dirt getting into the fuel system. It is important that the fuel rail is sealed off to prevent ingress of dirt and allow individual injectors to be blanked off to allow further diagnostic tests. Ideal for sealing off injector ports on the rail one by one to diagnose fuel system pressure loss.Internal thread and sealing cones: sizes 6 x M12 x 1.5mm & 6 x M14 x 1.5mm. Fits most common rail injection rail sizes. Essential kit for diesel fuel system high pressure diagnostics.