Credit to artist st.Krojak for his 3D-Model of the millenium eye: https://sketchfab.com/3d-models/free-millenium-eye-print-ready-yugioh-8f9df2111412497e819de029717ea59d

I halved the eye for easier printing without supports. Also, I hollowed both halves so that you could put metal/sugar/whatever inside to give it a heavier feel before glueing both parts together.

If you rather have the two halves tightly connected, use the threaded models and print the SET_SCREW to put between them. Screw it into any of the to halves and then screw the second half onto the first. If you still see a gap, try printing the screw a millimeter shorter to create more pull between the parts.

Anycubic

All-metal Mega