Lay it Flat 3

Press one disc against another and turn. There are 3 blades on each disc, mounted in a sloped angle. When pressed together and turned, the blades will tighten and lock at a certain point. This type of system will be needed to insure that the cap will always line up with the body of the bottle. Rubber bushing or washer might be needed for a waterproof seal.
Operation
Press release button to open the cover, which springs up via the rubber knob.