Since I already posted this once before to your post where you couldn't get the headlight cap off, and that post is gone.
The BPI on the G3 and G4 is on the right as you look at from the front of machine then on the G5 and later they switched it to the left side. The small cap goes to the side with the magnet and the large cap goes to the side without the magnet. Sometimes people will get the wrong brushroll so the magnet is at the wrong end. Then they can't understand why the BPI doesn't work.
The one you have looks like the original, the plastic is over the magnet so you don't see it.
Here's pics of my G4 head
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