Product selection
Reviewed by MAXILUB · 5 min read · Updated 2026-08-28
GL-4 and GL-5 are performance categories
API GL-4 and GL-5 describe different gear-lubricant service categories. They are not viscosity grades and should not be treated as interchangeable labels. The equipment manufacturer determines the required category. A product carrying GL-5 should not automatically be used where GL-4 is specified unless the product and equipment documentation explicitly support that use.
Match the SAE viscosity too
A gear oil requirement usually combines a service category with an SAE viscosity such as 75W-90, 80W-90 or 85W-140. The same service category can be available in several viscosities. Confirm both values from the manual, equipment label or service documentation before requesting a quote.
Manual transmissions and axles can differ
A truck, machine or vehicle may specify one lubricant for the transmission and another for the axle or final drive. Synchronizer materials, gear geometry and operating load can affect the requirement. Build an asset-specific lubricant chart so purchasing and maintenance teams do not assume that one gear oil covers every compartment.
What to send the distributor
Provide the required API category, SAE viscosity, equipment type, any OEM specification, quantity, package size and delivery ZIP code. If the requirement is unclear, send a photo or exact transcription of the manual specification rather than relying on a product color or brand previously used.