Abstract: A thermostatic expansible work element comprising a housing within which there is enclosed an expansible body. In the expansible body there extends the one pointed end of a work member in the form of a work pin or piston, the other end of which extends through an opening out of the housing. Between the opening and the end face of the expansible body which confronts such opening there is arranged a ring-shaped or annular disk which surrounds with a sliding fit the work pin or piston. The ring-shaped disk covers an annular space or gap between the opening and the outer diameter of the work pin or piston, so that the latter, during its displacement or stroke, also can be deflected out of its original axial direction without binding in the opening. The thermostatic expansible work element also can be externally heated so as to serve as a servo for remote actuation of an element, for instance valves.