serve as transition members between the core and the segments 20 they may be provided with vanes 19 and 30 that line up with the vanes 22 and 28 of the adjacent segments fig2 illustrates a way to attach the segments to core 21 and to each other for preventing rotation of the segments with respect to each other recesses 40 may be provided the top surface of the vanes as shown in fig2 pins 43 shown in fig3 are adapted to fit within recesses 40 in the lower surface of an adjacent vane to prevent rotation of the segments about core member 21 holes 42 are formed in the passageways between the vanes and extend to the inner surface of the segments a suitable set screw welded pin press weld pin threaded pin or any other known securing means can be inserted into the hole for securing the segment to the core member 21 it is understood that there are many other techniques and mechanisms that could be used to attach the various components to each other all of which could be used in the context of this invention upper collar member 18 may be welded to core member 21 or secured to it by any well known arrangement fig3 illustrates an arrangement of the segments and collars on the core the core includes an upper connection portion 12 known as an api connector and a lower integral portion 21 formed as a hollow cylindrical body upper collar member 18 and segments 20 have an internal diameter slightly greater than the external diameter of cylindrical portion 21 of the core so that they can slide over the outer surface of core portion 21 the exterior lower surface.