A nozzle assembly, for a metal casting apparatus selected from a sliding gate and a tube exchange device, comprises a first refractory element comprising a first coupling surface which includes a first bore aperture, and a second refractory element comprising a second coupling surface, which includes a second bore aperture, the first and second elements being coupled to one another in a sliding translation relationship through their respective first and second coupling surfaces such that the first and second bore apertures can be brought into and out of registry to define, when in registry, a continuous bore for discharging molten metal from a molten metal inlet to a molten metal outlet of said nozzle assembly. A sealing member is provided between the first and second coupling surfaces of the first and second elements. The sealing member comprises a thermally intumescent material.