Mini Blinds Bottom String Plug

This all started when my wife asked me to fix the blinds. With a 1 year old and mini blinds in reach they tend to get ripped up. Anyways, when i took the blinds down I had noticed that the plug that goes into the bottom of the mini blinds was missing. Then the idea to make one of my own popped up. With my minimal knowledge of openscad and my moderate knowledge in cad i started drawing. The plan was to use linear extrude in openscad but i couldnt figure out how to difference with it, maybe t