Retractable Pen (Fully-functional)

thingiverse

Here's a pen that retracts easily, and it works as expected. You'll need a spring and an ink refill, but the refill is thicker, similar to what you'd find in larger retractable pens - check out the images above for reference. The button piece can be fragile, so any suggestions on making it more durable would be greatly appreciated. Feel free to get creative with your own versions!