How do you fit the beer bottle in there to pop the lid though? Not a whole lot of space to be swingin' a bottle around the downtube/ seat tube/ chain ring.

I'd spill beer (party foul) all over the place with one of those. My design allows even a 22oz Fat Tire or 1554 bottle to be opened while being kept vertical to avoid spillage.

Photo for reference of why a cage mount wouldn't be very effective on my bike:


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hocdub- My original design was for an opener like yours (the ring shape) as a bar end plug on the left bar end. I couldn't get the welding/grinding to look exactly right on the prototype so I decided to do this instead.