Abstract: A hot dip coating pot (2) having a strip inlet passage (3) and electro-magnetic plugging means to prevent leakage of bath liquid form the pot through that passage, wherein: the plugging means comprises two magnetic field generator (7) disposed one on each side of the passage; each generator projects an oscillating magnetic field into the passage from at least two poles of opposite polarity that are adjacent the passage and spaced apart in the through direction of the passage; the said at least two poles of each generator are respectively in substantial alignment with the corresponding poles of the other in the transverse direction of the passage; the magnetic field projected by the generators have flux patterns which are substantially mirror images with reference to a plane of reflection coinciding with a centre plane of the passage; and both generators operate at a frequency of more than seven kiloHertz. When no strip is present the fields combine and extend transversely of the passage.