If you plan carefully it may work. There are keys made this way. It depends on the thickness of your key (for mine the thickness is the same as that of the main blade). Just keep your locks lubricated well (use graphite for that) as that assembly doesnīt allow for too much torque. I wouldnīt like the idea of having to carry that particular knife only because I need to have my key.
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If it isnīt broken, it doesnīt have enough features yet.