Abstract: A thermocouple housing having a ceramic protection tube with a closed end for immersion into a metal melt and an open end for receiving thermocouple wires. The ceramic protection tube has a reduced diameter portion spaced from the open end by a distance x. A metal protection tube having a threaded end and adapted at an opposite end for attachment to a connection head for electrical connection of the thermocouple wires to a meter for measuring a potential difference between the wires is connected to the ceramic protection tube by an adaptor. The adaptor comprises a hollow body having a through passage which receives the ceramic protection tube at one end and the metal protection tube at an opposite end, the through passage being threaded for coupling to the metal protection tube. A radially inwardly directed shoulder projecting into the through passage is spaced from the threaded end by a distance which exceeds x and is dimensioned so as to accommodate the open end of the ceramic protection tube.