These puzzle piece magnet heart pendants can either be worn as individual necklaces, like friendship necklaces or they can be put on one necklace and used as the way to clasp the necklace together. 

These are meant to be printed with a 3mm cube magnet, but I've also provided a version with no magnet spot and ones designed to fit 1/8" cube magnets as it seems the 3mm cube I bought ages ago seems hard to find, but 1/8" cube seems easier to find. When adding the magnet, pause it before the layer where it would close it in and add the magnet. Start the print back up to seal the magnet in. 

I did Hilbert Curve infill on top and bottom for texture, but you can use any texture and even use ironing if you want to make it smooth. 

More information on the design process on Instructables: https://www.instructables.com/Friendship-Heart-Necklaces/

Made in Tinkercad. Curved the heart in Fusion 360.