extent of the hook 504 the flanges of the spacer prevent the spacer from exiting the enclosure laterally the hook 504 therefore holds the spacer loosely in the enclosure so that the spacer can rotate about the cylindrical axis of the central trunk while being held by the hook 504 referring now to fig5 b a cutaway view of the insertion tool 500 of fig5 a holding the spacer 100 of fig1 a c shows the extent of the hook 504 in cross section and fitting within the annular groove of the spacer it can be seen that to enable the spacer 100 to be loosely held in the enclosure the width of the extent is smaller than the width of the annular groove and the depth of the extent is less than the depth of the annular groove if it is desirable for the flanges to fully flank the extent preferably as shown the outer diameter of the hook 504 is substantially equal to the outer diameter of the spacer 100 referring now to fig6 a b an embodiment of a loading accessory 600 for a spacer insertion tool of the invention is illustrated in side and top views respectively the loading accessory 600 can be used to ease the passing of the central trunk of the spacer through the opening of the spacer insertion tool both for loading the spacer into the enclosure and unloading the spacer from the enclosure the loading accessory 600 includes an elongated shaft 602 and a forked hook 604 at an end of the shaft 602 a notch 606 having a base 608 separates the tines 610 612 of the forked hook 604 the width of the notch 608 separating the tines 610 612 is wide enough.