Shell designed to be glued on 14mm clothing press button.
It is to be used as a EMG/ECG electrode to sense muscel activity or heart beats.
Follow this tutorial on how to make the electrode and simply glue the top of the button into the shell. The tutorial also displays a way to know to place the electrodes and a easy way to create a conductive gel.

Tutorial: http://www.instructables.com/id/How-to-make-ECG-pads-conductive-gel/?ALLSTEPS

Do not use homemade electrodes for medical testing.