I may just be adding to the confusion here.... Picture a mast sitting on a level plane with it's chainplates such that the pins are in line with the mast step bolt that the mast pivots on. Obviously the whole thing would allow the mast to fold for or aft as if it were a hinge. However, if you move the chainplate pin away from this pivot point the geometery changes so that as the mast is lowering it is either applying tension to the shrouds or compression (ie, the shrouds go slack). Unless everything is kept in line you cannot have the upper shrouds keeping the mast in column as it pivots for or aft. The purpose of the extensions is to pring this pivot point up in line with the pivot of the mast. The bridles are attached to the extensions (and led to the toe-rail or padeyes or the like) to keep their fore and aft positions constant. This setup allows the mast to be stepped and unstepped as if all the pivot points are in plane.
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