therein only one aperture 11 is shown in fig1 but in fig2 an adjacent aperture 11 39 is shown apertures 11 comprise holes 12 drilled or otherwise cut through the casing all being equi angularly spaced about the casing axis each hole 12 being provided with cut out slot portions 14 on diametrically opposing sides e g by a milling or grinding process so as to effectively form a diametrically extending slot 15 during construction of the turbine vanes 16 can only be inserted through the turbine casing 10 by engaging the leading and trailing edges l t of their aerofoil portions 17 with the slots 15 i e cut outs 14 and pushing the vanes radially inwards the vanes 16 have spindles s at their outer ends shown only in plan view in fig2 and after being pushed fully home each vane 16 is supported by its spindle s in a bearing and sealing assembly 18 for pivoting movement about an approximately radially extending pivot axis a this bearing and sealing assembly 18 also obturates the hole and slot arrangement 12 15 and has a housing 19 which is bolted to the casing 10 to secure the assembly the vanes and slots are judiciously configured and dimensioned with respect to each other in particular each slot 15 is aligned and shaped so as to only accept the radially inner end of a vane 39 s aerofoil portion when that vane is presented in an attitude which closely approximates its attitude in one extreme part of its operational pivotal movement preferably this attitude is.