ISO VG – ISO Grade (where ISO is the International Standards Organisation) – the higher the VG number the more viscous the fluid is. The VG number tells you which hydraulic oil is thicker. This is sometimes referred to as the hydraulic oil weight. At the same time, grades with a W next to them indicate the weight (Unlike automobile engine oil which refers to winter oil).
AGMA Grade – American Gear Manufacturers Association – Leaders in the standards of gear oils.
SAE – Society of Automotive Engineers
In the UK, ISO VG is used mainly for grading hydraulic oil. Below is a list of common hydraulic oil ISO grades and a general guide to their applications:
%tick% ISO 100 Hydraulic Oil – ISO VG 100 Hydraulic Fluid tends to be used in industrial machinery with heavy loads.
%tick% ISO 15 Hydraulic Oil – ISO VG 15 Hydraulic Fluid is typically used in power steering and hydraulic brake systems.
%tick% ISO 22 Hydraulic Oil – ISO VG 22 Hydraulic Fluid is generally used in airlines for air tools etc.
%tick% ISO 32 Hydraulic Oil – ISO VG 32 Hydraulic Fluid is ideal for use in high-powered machine tools.
%tick% ISO 46 Hydraulic Oil – ISO VG 46 Hydraulic Fluid is normally required for industrial plant working under high-pressure etc.
%tick% ISO 68 Hydraulic Oil – ISO VG 68 Hydraulic Fluid is designed for use in systems which require a large load-carrying ability.