We have several Airflow Icon extractor fans around our house, and visitors inevitably snap the cord when they try to turn on the fan using the pull cord. This is because, by design, there is no snap action in the switch and despite the warning label, people tend to pull until they feel the "Click," which doesn't happen and they keep pulling until either the frangible link breaks, or they snap the cord / break the switch module. If you have one of these fans with a pull cord module, you'll likely know what I'm on about.
So, I decided to create this break-away coupler, to save me having to buy another module, or make my guests go and use a nearest available tree in my garden.
A pretty simple print, it's designed to house a 6mm diameter by 4mm long neodymium N42 magnet. It is designed to be printed with the mating face to the build-plate with no supports. I used 30% infill, printed in PLA+ for now but might make a set out of PETG later. It goes without saying, you need to print a pair for each pull-cord.
I had to experiment with magnets as the stated pull force stated on the websites I found to be pretty optimistic to be honest. I measured the fan pull-cord force required to reliably operate the switch and it proved to be around 700grammes (Just over 1 lb). The N42 6mm x 4mm I used here were rated at 1.1Kg but I measured with a spring balance and they were less than 1Kg. If you find them a bit weak, you could experiment with N52 magnets of the same size, which are supposedly stronger, or use 6mm x 6mm long magnets but you may have to stretch the model in your slicer in Z axis, to give sufficient clearance to fish the cord through. Link to the magnets from Amazon below, along with additional cord at 1.0mm diameter.
https://amzn.eu/d/bburScJ
https://amzn.eu/d/63d0igg