upon in a direction toward the biasing diaphragm spring 4 and hence axially in a direction toward the housing 2 the diaphragm spring 13 which is installed between the pressure plate 3 and the biasing diaphragm spring 4 comprises a ring shaped main body portion 13b and the aforementioned outwardly projecting sections or tongues 13c which project radially from the outer marginal part of the main body portion 13b and constitute the seat 11 the radially inner part of the main body portion 13b is provided with arms 13d which cooperate with abutments 14 fig2 being of one piece with the housing 2 a connection or lock resembling a bayonet mount is provided between the abutments 14 and the arms 13d of the diaphragm spring shaped structural element 13 once the diaphragm spring shaped structural element 13 has been prestressed in the axial direction and its radially inner portions 13a or its arms 13d have been placed axially over the abutments 14 an appropriate angular movement of the diaphragm spring shaped structural element 13 relative to the housing 2 ensures that the arms 13d of the structural element 13 can be moved into engagement with the abutments 14 in order to prevent rotation of the biasing diaphragm spring 4 relative to the housing 2 the latter.