A magnet assembly for attracting and retaining ferrous particles in liquid fuel comprises a plurality of magnets arranged on a mounting side by side at a spacing; adjacent magnets have oppositely directed north/south axes. The arrangement provides an enhanced magnetic field on the magnet side of the mounting, and a weakened magnetic field on the opposite side. The magnets are coated to prevent corrosion thereof by fuel. The assembly may be housed in a moulded plastics case defining spaced chambers for the magnets.
