How to Order Tenebraex caps and ARDs: Tenebraex caps do not mount like other available caps. To properly mount the Tactical Tough (TT) objective cap(LINK), either a TT Adaptor (LINK) is required or a TT compatible ARD (LINK). The objective cap will not mount to the scope without one of these items.
The ocular (rear) caps come as a complete unit (adaptor and cap) that attaches directly to the scopes ocular end.
The adaptors actually provide a valuble function. They allow the caps to rotate freely 360 degrees to account for left/right hand shooters, rotating ocular of Nightforce scopes, scope-to-barrel clearance issues, bolt clearance issues etc.