It’s all about the snap. Will also hold a jellybean or small chocolate.

See here for video: https://youtu.be/p5RxgP4WY7Y

See here for stable download: Egg Snaps: https://than.gs/m/810065 The best way to print these is as oriented, with the model raised off the build plate 3mm and tree supports underneath. You will likely need to smooth the surfaces. If they are too tight, snapping them together and apart a few times will loosen it up.

Other snap-together eggs: Basketball: https://thangs.com/mythangs/file/796742 Tennis Ball: https://thangs.com/mythangs/file/796748 Baseball: https://thangs.com/mythangs/file/796753