API GL-4 - oils for operating in different conditions - from light to heavy. They contain 4.0 % of effective antiscuffing additives. The oils are designs for bevel and hypoid gears which have small displacement of axes, for gearboxes of trucks, for units of axles. These oils are recommended for not synchronized gearboxes of US trucks, tractors and buses, for main and other gears of all vehicles. Now these oils are the basic for the synchronized gearboxes, especial in Europe.
API GL-5 - oils for the most loaded gears, working in severe conditions. They contains up to 6.5 % effective antiscuffing additives. The general applications of oils this class - the hypoid gears having significant displacement of axes. They recommended as universal oils to all other units of mechanical transmission (except gearboxes). The oils which have special approval of vehicle manufacturers can to use for synchronized manual gearboxes only. API GL-5 oils can be used for limited slip differentials if they correspond to requirements of specification MIL-L-2105D or ZF TE-ML-05. In this case the designation of class will be another, for example API GL-5+ or API GL-5 LS
