Extruded tubes are classed as primary kiln furniture and are used as supports for plain and extruded batts. They are made by high pressure vacuum extrusion and occasionally by pressure casting. Extruded tubes can be split into six sub-categories based on shape and length as follows: Long Extruded Tube, Round Extruded Tube, Elliptic Extruded Tube, Square Extruded Tube, Rhomboid Extruded Tube and Special Extruded Tube.