Abstract: Refractory, gas-permeable bubbling plugs for a vessel containing a molten metal have a cold end remote from the molten metal and a hot end facing the molten metal. The hot plug end is subject to wear by the heat radiated from the molten metal to leave a remaining plug size after wear, and such plugs comprise at least one measuring probe displaying the remaining plug size. According to the invention, the measuring probe comprises a small tube having a tip extending into the plug and spaced a predetermined distance from the cold plug end, and an end section protruding from the cold plug end, a wire movably mounted within the small tube, a spring preloading the wire, a connection connecting an end of the wire to the tip of the small tube and detachable by the effect of the radiated heat, and an optical display unit attached to the wire in the protruding end section of the measuring probe tube.

Abstract: A gas-permeable element of a refractory material for blowing gases into a metal treatment vessel through its lining has a body of a refractory material, a metal housing on the longitudinal sides of the refractory body, a free inner end surface at which the refractory material is exposed, an outer end surface provided with a gas distributing chamber for a gas supply, at least one local opening extending in the interior of the refractory body for a gas passage between the end surfaces and provided with a metal insert, wherein the metal insert is formed as a laterally closed small channel, the gas-distributing chamber is separated from the refractory material by a metal sheet plate, and the metal channel is tightly mounted in the metal sheet plate so that the refractory material is maintained free from loading with a gas pressure.