To AS -- I believe the OP is describing a pinch bolt washer with bent tabs extending from it, as was (is?) common on many Shimano derailleurs.

To the OP -- hopefully I've properly translated your description and AS can give you specific info since he's far more familiar with various Shimano designs than I am. But the general rule for cable routing is for the wire to be roued as far out on the swing arm as possible, and under the side of the pinch bolt farther from the pivot. You might even see a groove or discoloration on the arm where the cable used to be.