Angle grinder 4 1/2″ diamond blade with 7/8 in. with 5/8 in. insert included -what is the insert for

I have a 4 1/2" angle grinder and I bought this blade because I need to cut some concrete bricks for my patio.

With the blade I received a small disk that fits in the hole of the diamond disk and it seems to be some sort of adapter so that the blade can match the size of the arbor.

When I tried to attach the blade that seemed to be the only way to attach it (by using this small disk) but when it did not really work, the blade did not seem to attach firmly to the arbor even after I tightened the screw that was supposed to press both the blade and the adapter (the piece with three small wholes in the picture)

I am talking about the yellow disk labeled "Adapter" below. (I represented this based on what I remember about it, I don't have the tool in front of me)

What am I doing wrong?

Edit: I have checked and indeed if you flip the nut then the nut presses on the disk. If the nut is not flipped the nut pressed on the adapter. The nut in this last mentioned position is used when you have a recessed blade that you use angled for grinding.

The adapter is needed to center the blade on the arbor BUT it has not role in in the tightening mechanism that keeps the blade in place. That it the role of the nut if it is flipped