<P> API Category GL - 5 designates the type of service characteristic of gears, particularly hypoids in automotive axles under high - speed and / or low - speed, high - torque conditions . Lubricants qualified under U.S. Military specification MIL - L - 2105D (formerly MIL - L - 2015C), MIL - PRF - 2105E and SAE J2360 satisfy the requirements of the API GL - 5 service designation . </P> <P> API Category GL - 6 (inactive) designates the type of service characteristic of gears designed with a very high pinion offset . Such designs typically require (gear) score protection in excess of that provided by API GL - 5 gear oils . The original API GL - 6 test equipment is obsolete . </P> <P> API Category MT - 1 designates lubricants intended for non-synchronized manual transmissions used in buses and heavy - duty trucks . Lubricants meeting API MT - 1 provide protection against the combination of thermal degradation, component wear, and oil seal deterioration which is not provided by lubricants meeting only the requirements of API GL - 4 and API GL - 5 . </P> <P> MIL - PRF - 2105E this specification released in 1995 combines the performance requirements of its predecessor (MIL - L - 2105D) and API MT - 1 . MIL - PRF - 2105E maintains all existing chemical / physical requirements, stationary axle test requirements, field test requirements and data review by the Lubricants Review Institute that were required under MIL - L - 2105D . It also adds the stringent oil seal compatibility and thermal durability test requirements under API MT - 1 . MIL - PRF - 2105E has been re-written as SAE Standard J2360 . SAE J2360 standard is a new global quality standard that defines a level of performance equivalent to that defined by MIL - PRF - 2105E, a U.S. military standard for approval that was not available to oil blenders in all parts of the world . It includes all of the most recent axle and transmission testing requirements identified in API GL - 5, API MT - 1, and MIL - PRF - 2105E including the need to demonstrate proof - of - performance through rigorous field testing . </P>

What is the difference between gl4 and gl5 gear oil