Originally Posted By NANKET
Master cylinder lid clamp. Manual brake with bolt on lid. That center square has been added.


Thanks NANKET! beer

So the center square (which is a threaded nut upon a closer look) was added on? Well that makes sense if the brake master clamp bolt catches the threads on the reservoir, there would be NO need for the clamp to have threads for the bolt.

Maybe someone was making sure that the clamp wouldn't come loose by having two thread sources for the bolt??

Anyway thanks again, what time era/make/model/platform are we talking here?