This is 3-piece toolbox concept, to be mounted on standard bike bottle cage inserts. The bracket is to be bolted on the bike frame, where a typical bottle cage would be installed. Then, the top shell slides and turns into the bottom shell with a quarter turn (no stop). Finally, both shells, once aligned properly, slide into the bracket and lock. The bracket holds everything in place with a stop that can be released with a flexible tab.
Initially, I intended to install a battery pack in there for my light, so there is a hole in the top shell that gets obstructed with a plug, once the light cable goes through.