Abstract: A mold cassette and method for continuously casting thin slabs. The cassette comprises a trough including a pair of vertically disposed, opposed broad walls and a pair of opposed narrow walls. The trough has an entry end for receiving molten material and an exit end for dispensing the material. The narrow walls are generally wider at the entry end than the exit end and are adapted for sealing engagement with the broad walls so as to prevent leakage of the material therebetween. At least one of the narrow walls is oriented at a selected tilt and adjustable at the tilt for changing the width of the slab during casting. Back edges of at least one of the adjustable narrow walls are relieved a region corresponding generally to the transition zone of the trough. This allows positioning of the narrow wall in a generally less than vertical plane during casting while maintaining the broad and narrow walls in sealing engagement with one another.