br0qn
Retro Guru
Top picture and bottom picture are two different mounting styles but not inclusive of each other. Both photos represent Shimano-style. The top picture is used for older down tube shift levers. The post sticking out acts as a stopper so the shifter lever does not over rotate causing a chain to skip the largest gear on the cassette/freewheel and wedge in between the spokes. You want the "over rotation tab" to point up toward the head tube when installing.
The lower picture is a flush-mount adapter to "fit" the contour of the downtube and works with newer shifter levers like Dura Ace 7400 for example. The non chrome side that integrates with the shifter is also designed with a stopper - the widest tooth. Kind of like a Shimano cassette where there is one wide tooth to ensure alignment on the freewheel. Idiot proof to get the shifter on one way only.
Gotcha, that all makes sense. I was a bit miffed when the tabbed washer didn't seat properly on the boss. It's square at the base of the boss but the welds kind of keep the washer from biting. But...I felt I was overdoing it with the thumbscrew so I just stopped before I ruined something. Better to find some guidance.
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