Help With Removing Bar End Mirror Inserts

Try loosening the fastener a few turns then tap the end of the fastener with a mallet which should free the insert?

 

It's an expanding anchor bolt type fastener. Screw the bolt back in a few threads (about 6mm) then tap the end of the bolt with a rubber mallet / hammer until it pushes the insert free inside the bar. You should then be able to pull out the whole assembly.

 

It's welded in leave it there. Use it to fit new mirrors or bar end weights.