Mirrors to see BEHIND you? What a novel idea for a motorcycle. I have a set of mirror extenders on my other bike. I may have to see it they fit my Sportster. Does the Sportster have a reverse thread on the right hand mirror?
I'm not exactly sure where I got my extensions but I think it was from the Dealer. Your mirror screws into the extension and the extension screws into place were the mirror was attached. I used red treadlock and you couldn't hardly tell I had used the extensions on my 1200 Custom but they sure did help.