2nds due to chipped edges of the bricks - please see picture for details which gives a better understanding

These Supra diatomaceous insulation bricks are for the majority Silica based and have an excellent cold crushing strength typically of 7.5MPA . The Molar bricks have a maximum service temperature limit of 950 degrees Celsius. Generally these refractory bricks are used under Firebrick Hearths or as backup insulation lining, though can be used on the hot face in certain applications. Typical analysis sheets are available upon request