This is a simple print-in-place design with hinge and catch to hold it closed.

It fits a Seydel Lightning harmonica. It may hold other brands but I have not tested. It does not fit Seydel Session Steel or the Classic Bold Body models.

It will feel stiff the first time you close it, but it loosens up immediately.

It’s very easy to modify this to have the key signature integrated into the lid for quick identification. 

Let me know what modifications you would like to see.