Brake fluid is a type of hydraulic fluid used in hydraulic brake and hydraulic clutch applications in automobiles, motorcycles, light trucks, and some bicycles. It is used to transfer force into pressure, and to amplify braking force. It works because liquids are not appreciably compressible. Most brake fluids used today are glycol-ether based, but mineral oil (Citroën/Rolls-Royce liquide hydraulique minéral (LHM)) and silicone-based (DOT 5) fluids are also available. Standards Most Brake fluids are manufactured to meet standards set by international, national, or local organizations or government agencies. International The International Standards Organisation has published its standard ISO 4925, defining classes 3, 4, and 5, as well as class 5.1, class 6 and class 7 reflecting progressively higher performance for brake fluids. SAE The Society of Automotive Engineers SAE has published standards J1703, J1704, and J1705, reflecting progressively higher performance for brake fluids. These have counterparts in the international standard, ISO 4925. United States The Federal Motor Vehicle Safety Standards (FMVSS) under FMVSS Standard No. 116 defines grades DOT 3, DOT 4, DOT 5 and DOT 5.1, where DOT refers to the U.S. Department of Transportation. These are widely used in other countries. Their classifications broadly reflect the SAE's specifications, DOT 3 is equivalent to SAE J1703 and ISO class 3, DOT 4 to SAE J1704 and ISO class 4, etc. All DOT compliant fluids must be colorless or amber, except for DOT 5 silicone, which must be purple. FMVSS Standard No. 116's scope is limited to fluid 'for use'. Brake fluid 'in use', or not labeled DOT compliant, is found any color. DOT 4 While a vehicle that uses DOT 3 may also use DOT 4 or 5.1 (a temperature upgrade) if the elastomers in the system accept the borate compounds that raise the boiling point, a vehicle that requires DOT 4 might boil the brake fluid if a DOT 3 (a temperature downgrade) is used. Additionally, these polyglycol-ether-based fluids cannot be mixed with DOT 5.0, which is silicone based. DOT 5 DOT 5 is a silicone-based fluid and is separate from the series of DOT 2, 3, 4, 5.1. It is immiscible with water, and with other brake fluids, and must not be mixed with them. Systems can change fluid only after a complete system changeover, such as a total restoration. It contains at least 70% by weight of a diorgano polysiloxane. Unlike polyethylene glycol based fluids, DOT