OK let me try to put my observation forward again.
The shackle pin is touching the bush from inside of the bush. The leaf spring (shah patta) is touching/ holding the bush from it's outside. Now the bush never moves/ rotates in the shackle/ shah patta. It is the pin which rotates/ moves in the bush. So no matter how much you tighten the nut of the pin, it will never allow both the shackles to touch the leaf spring as the pin has collars to hold the shackles. The nut can only break down or can damage the rings (choori) of the pin.
For example if the width of the leaf spring is 3 inch, the shackles will never be able to come closer than 3.25 inch (approx), no matter how much pressure you apply on the nut. And this .25 inch gap is exactly covered by the sides of the bush.
Your understanding on the above is required.