The 10 specially shaped 'bricks' were made with a cement able to withstand temperatures to around 1800C. These are part of a steam locomotive's firebox. It is called the brick arch. The upper level text denotes the types of locomotives which this set of molds is used in.

When installed they form an arch over the forward part of the fire. They create a longer path for the flame from the coal burning on the grate to the tube plate of the cylindrical part of the boiler. This enables more energy to be obtained from the coal used. They also cause the fire's heat to be more evenly spread over the tube plate thus reducing stresses in the metal while heating and cooling. March 2024.