The present invention relates to a Measuring insert (3) for determining and/or monitoring a temperature (T) of a medium (M) in a vessel (V) or pipe for insertion into a protective tube (2) which protective tube (2) at least partially protrudes into an inner volume of the vessel (V) or pipe,the measuring insert (3) comprising an elongated tube (3a), and a temperature sensor (5) arranged inside an end region of the measuring insert (3). According to the present invention the measuring insert (3) further comprises a coupling element (9) fastened to the elongated tube (3a) in the end region in which the temperature sensor (5) is arranged, which coupling element (9) is embodied and/or dimensioned so as to serve for fixing the measuring insert (3) inside the protective tube (2) in a state in which the measuring insert (3) is introduced into the protective tube (2).