It is the Society of Automotive Engineers standard for fuel and oil hose. R6 designates a general-purpose reinforced hose suitable for petrol, diesel and lubricating oils at low to moderate pressure - the specification most automotive fuel lines are built to. It is the rating to look for on anything carrying hydrocarbons.

Everything in our range built to that standard - fluorolined silicone straights, couplers, 45 and 90 degree elbows, long leg elbows and Classic Wrapped hose; rubber multi-purpose, cotton braided, steel overbraid and unreinforced fuel and oil hose; and the vehicle-specific fuel filler neck, tank breather and fuel pump hoses for VW, Ford, Land Rover, Range Rover, MG, Fiat and Peugeot.

Our J30 R6 products are formulated for modern ethanol-blended fuels as well as diesel and oils. This matters a great deal on older vehicles: ethanol attacks unsuitable rubber from the inside, so an original fuel line can look perfectly sound externally while degrading internally and shedding debris into the fuel system.

Because standard silicone and EPDM rubber both swell and break down in contact with petrol, diesel and oil. They are excellent coolant and air materials and completely wrong for fuel. The failure is gradual and internal, so it does not announce itself - which is exactly why the specification matters rather than the appearance.

Yes, and it should be used there. A crankcase breather carries oil mist, which will destroy plain silicone over time even though nothing liquid is obviously flowing through it. Breather and catch-can plumbing is one of the most common places people fit the wrong hose. Use J30 R6 fluorolined silicone or rubber.

Fluorolined silicone runs -60C to +180C, will not perish with age, and is available in moulded elbows and shapes. Rubber to J30 R6 is cheaper, matches the original look, and is the practical choice for a straightforward like-for-like fuel line replacement. For a hot engine bay or an awkward position, silicone is worth the extra.