This thing was made with Tinkercad. Edit it online https://www.tinkercad.com/things/f6KPB7bB1hR
I have trouble with light getting through the gap in my curtains, so I built this clip to keep the top of the curtains clipped together, works a treat.
The spring is quite strong but flexible as my curtains are quite heavy.
I used a circle, box and triangle basic shapes to create this. Printed using PLA at 220c.