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1. There was a small gap left between my fairing and the mirror plate, so my fairing and windscreen flapped. So I cut off the bottom portion of the rubber piece of my old factory mirrors and that gap went away. You can probably use nylon washers between the fairing and the block off plate.
2. I bought these mirror base plates to fill the holes exposed by the removal of the mirrors on my 2004 for Yamaha R6. They were very simple to install and snug fit in place and don't seem like they're going anywhere.
3. The block off plates fit flush without gap and they don't look out of place and there's no vibration or rattling to be heard of. Didn't come with nuts to tighten though.