This is a fishing bobber that I have designed for the Make It Float Challenge. It has taken many revisions to get a model that I'm happy with. My major revisions for the bobber and lock are shown with earliest revs on the left and finished revisions further to the right. Although all of the bobbers and locks worked, my revisions were aimed at becoming lighter, stronger and easier to print. Incorporating the extrusion in the bobber to other hollow models it is likely that you could make almost anything into a Bobber with the same locking mechanism.