Abstract: Fitting of a fluid temperature switch unit of the kind including an enclosure having an end face at one end and a bimetal disc at the other end, in a chamber containing a fluid and having a wall comprising a recess having a bottom-face formed with an opening leading into the chamber. The bottom-face is covered by a metal plate, and the opening is sealed by urging the metal plate toward the recess wall, while the end of the unit containing the bimetal disc is pressed against the metal plate.