Out of the box the MTC Vipers and Mambas have an adaptor ring attached to the front of the scope that needs to be removed if the sunshade is to be fitted. That ring will then attach to the front of the sunshade so that the flip up cap can be attached to the front of the sunshade. If your scope has the flip up cap attached to the front of the sunshade then just remove the adaptor ring and reattach it to the front of the scope.
A.G