I changed the dimensions of the spring retaining ports to be used with standard pen springs.
The original design is awesome, but I didn't have any of the springs the original designer used. So I changed the design slightly to accommodate the use of a single spring out of a standard ballpoint pen. I used a spring out of a Zebra brand ballpoint clicky pen. Cut the spring in half and use one half in each side.
BOM:
The author remixed this model.