it possible to construct the pins of a highly heat resistant metallic material instead of ceramic as in fig1 it is also possible to employ a single retaining pin as this will secure body 27 to member 28 in fixed angular position member 28 has an outer end flange 31 facing axially juxtaposed member 29 a thermally insulating annular sealing means is interposed at both radial faces and at the circumference of the outer end flange 31 in a recess in the cylinder head 14 on the one hand and between the menber 29 on the other hand the sealing means comprises three gasket rings 32 33 and 34 which serve to thermally insulate the member 28 from the member 29 and cylinder head 14 and reduce the flow of heat from member 29 to member 29 and cylinder head 14 thereby minimizing thermal stress in member 28 and body 27 secured thereto due to thermal gradients the rings 32 33 and 34 also perform a concomitant function namely in order to relieve thermal and mechanical stresses in the member 28 the axial preload exerted by the metal member 29 is mainly transferred to the cylinder head via the conical surface 16 and due to the presence of the rings 32 33 and 34 only part of the clamping pressure that is applied by the metal member 29 through the bolts 18 comes to bear on the ceramic member 28 and especially the end flange thereof this prevents the member 28 from bursting apart in fig5 and 6 a modified cnstruction is shown wherein the ceramic baffles in fig1 and 3 are replaced.