From Ronald in Texas:
Review: The need for a quick-release plate to attach a camera or spotting scope to a tripod head adds a mechanical weakness that often leads to loosening, and often at inappropriate times. The plate design is intended to attach a variety of different cameras, telephoto lens and spotting scopes to the tripod head, and some combinations are more successful. My particular combination of a Manfrotto tripod head, quick-release plate and Zeiss spotting scope is not ideal. The plastic pin supplied with the plate is too small for the second opening in the Zeiss mount and allows play when the plate loosens slightly. My solution was to thread the second hole and add an Allen set screw that better secures the plate to the scope.
Eventually manufacturers of tripods and spotting scopes will collaborate on universal designs for quick-release features and even design without the need for the plate, as at least one spotting scope manufacturer has done with its line of tripods.
My two cents: Another solution to throw into the mix, for those of you without scopes and tripod heads that match up well without a QR plate (Manfrotto's 3130 or 128 RC heads and Leica and Swarovski's current scopes) or have no problems loosening on a QR plate. It's not cheap, but the Manfrotto Anti-twist Spotting Scope Plate will solve your problems forever. Well worth the cost!