Knob for 1/4" flatted shaft

This is a work in progress, I want to add a spring in it to make it a one-piece push on and stay on knob. As is, this would be a good item to customize for your own use or just use it with a drop of glue in it to hold it on the shaft.

I added the locking sping in this thing: http://www.thingiverse.com/thing:97906