A cord pull for curtains and light switches. The OpenSCAD file is parametric so you can adjust the various dimensions to suit your needs. The example STL is a chunky 40mm tall, 25mm across, with a 3mm hole.

I've finally got around to making the useful household objects I promised my wife!

Modify the OpenSCAD parameters (at the top of the file), print and attach.

OpenSCAD is great for simple things like this, but it's a language only its author could love. For complicated designs it's like painting with a spork!