I never did understand the "adapters" aspect of it. Twice now I have changed out my mirrors to Harley style mirrors and all I did was select the bolt that came with the mirrors that was long enough and either wrapped electical tape or the last time I used shrink tube to make a "crush washer" so to speak and bolted them up. The tape or shrink tubing crushed into the mounting hole and made them rock solid... no movement or vibration at all. Hope that made sense.
