For breaking into fuel lines and hoses fitted with quick release couplings. 3 sizes fit popular makes of vehicle. Blue: 1/2" - 5/16" (8mm) for petrol engines: Ford, Dodge, Chrysler and Renault. Green 3/8" (10mm) for diesel engines: Ford, Dodge, Chrysler and Renault. Red for GM, Chevrolet, Buick, Pontiac, Renault, Fiat, Ford and Opel.