44 of the set of vanes 32 which are received by a set of upper and lower apertures 46 in the upper wall portions 48 and lower wall portions 50 respectively of the housing 22 the apertures 46 are preferably located at diametrically opposite sides of the housing 22 the apertures 46 may be semi circular as shown or rectangular and dimensioned to provide a snug fit between the apertures 46 and the appendages 42 the apertures 46 are partly defined by aperture wall portions 52 which are preferably straight to engage the corresponding appendages 42 which are similarly straight or flat the apertures 46 and more specifically the wall portions 48 and 50 are angled such that they are inclined relative to the axis 23 the angle of inclination of the apertures 46 and the upper wall portions 48 are preferably six degrees with reference to the axis 23 the angle of inclination of the apertures 46 and the lower wall portions 50 are preferably also six degrees with reference to the axis 23 since the apertures 46 and appendages 42 and their corresponding vanes 32 snugly interfit the angle of inclination of the apertures 46 translates to the same angle of inclination of the vanes.