I designed this ear plug case to be printed flat in pla plus with no supports to make it as user friendly as possible. I wanted it to be printed flat so that text (initials etc) can be added easily without a bunch of color swapping. It takes two 8mm x 3mm magnets. If you put a magnet on a hard surface and then press the internal component down, it will press in. Then stick the second magnet to the first and slide it into the cover and press down to insert it using the internal part as a tool and ensuring that you have the polarity correct. The press fit is good but a dab of super glue on the back of each magnet will help ensure they don't come out. I put a link to the correct size magnets below, thanks for looking!

TRYMAG 200Pcs Refrigerator Magnets, Small Round Magnets for Crafts, 8x3mm Mini Rare Earth Magnets Tiny Strong Neodymium Disc Magnets for Whiteboard, Fridge, Office, Hobbies, and Button Magnets: Amazon.com: Industrial & Scientific