Heater protective tube for molten metal holding furnace

A heater protection tube for use with a molten metal holding furnace, the molten metal holding furnace comprising

• a furnace body including a bottom wall, a ceiling wall, and a side wall extending between the bottom wall and the ceiling wall to form a molten metal containing space defined by the bottom wall, the ceiling wall, and the side wall, the furnace body including at least one insertion hole formed to extend through the side wall or the ceiling wall;
• and
• a heater protection tube including a heat generator and inserted in the insertion hole,
• the molten metal holding furnace for holding a molten metal contained in the molten metal containing space at a predetermined temperature by using heat generated by the heat generator,
• wherein the heater protection tube includes a distal tapered cylindrical portion corresponding to an inside tapered cylindrical portion and a proximal non-tapered cylindrical portion corresponding to an outside non-tapered cylindrical portion,
• the heater protection tube is configured so that it can be mounted in the side wall with the distal tapered cylindrical portion located at the inside tapered cylindrical portion and with the proximal non-tapered cylindrical portion located at the outside non-tapered cylindrical portion, and
• wherein the inside cylindrical portion of the insertion hole has an inner diameter discontinuously increasing from inside to outside of the furnace.