Some models do need an adaptor plate
Short or CanAm BRP extension : Many BRP models need the short extension plate to extend the top mounting bracket to reach the rear rack. The plate can also be used where there is a special need to gain extra room between the the rear rack and the Quadbar. Note that this can only be used (and useful) when the tow bar /hitch is also protruding out, close to the line of the rear rack.
Polaris 400/ 570 Sporsman & 400 hawkeye (2011 on) adaptor plate. Fits around the tool box.(see Polaris image) Only for the above models that look like the rear view picture .
Long Extension is only extreme cases where on other option is available. like the Polaris with the tipping tray.