I needed a set of magnetic checkers for an empty Ohio Art checkers tin. I had previously embedded magnets in a wooden Chess set but I couldn't get the magnets to work with the wooden checkers. I realized it would be easiest to design hollow checkers and drop a magnet into them during a paused print. I used 4.5 mm sphere magnets that were on hand and they proved strong enough. The checkers will stick to the tin and also stick to each other when crowning.