recess the free end faces 19 of the two root plates are of curved design for contact with the radial parts of the recesses the curvature is here selected in such a way that the contact points are always located on one line which is within the blade profile in order to ensure this under all operating conditions a defined clearance 20 between the arcuate peripheral surfaces 18 and the corresponding walls of the recess 15 is provided in the case of expansions caused by the temperature of the inlet flow housing and of the blade carriers 5 fixed thereto the radial parts of the recesses can thus roll over the curved end faces of the root plates the compressive stresses arising are absorbed by the blade leaf without the latter buckling out this is especially important in the case of a 360 u00b0 spiral according to fig1 since such spirals show varying expansion around the periphery if such unhindered expansion were not allowed for example as a result of unduly firm clearance free clamping of the root plates in the recesses it would be possible for the radial vane row to be overstressed since the flexural stress would also have.