ISO 4404-2:2010 specifies a procedure for the determination of the corrosion-inhibiting properties of non-aqueous hydraulic fluids within the category HFD, as classified in ISO 6743-4.It provides a qualitative assessment of corrosion of five of the most common metals used in the construction of hydraulic systems, but other metals and/or alloys could be added or substituted for these metals for particular installations.