Abstract: Elongated finned backup rollers have multiple magnetized fins for rolling contact with a moving endless, flexible, thin-gauge, heat-conducting, magnetically soft ferromagnetic casting belt for guiding and stabilizing the belt against thermal distortion while it moves along the mold cavity being heated at its front surface by heat from molten metal while being cooled at its reverse surface by flowing liquid coolant. Each finned backup roller includes an elongated, non-magnetic shaft rotatable around its axis and having multiple annular fins of magnetically soft ferromagnetic material fitted onto the shaft spaced along the shaft. The fins have circular perimeter rims for rolling contact with the reverse surface of a belt. Intervening collar shaped reach-out permanent magnets are mounted on the shaft between successive fins. The fins and reach-out collar magnets alternate in sequence along the length of the roller. The reach-out collar magnets are magnetized in a direction parallel with the axis of the roller.