I couldn't find the part I was looking for to fix my window blind. So I made this round thing for the end of the cord. The other item pictured is the:
Roller blind pull string fastener by GalFisk
Published on April 21, 2017
www.thingiverse.com/thing:2256170
(which works great, just need to ream out the hole a little, depending on the thickness of your cord).
Free for commercial use, have fun!