Just recently got my first bjd factory doll and wanted better neck positioning. Mocked this up in a few days. Print pieces separately on bed and then snap together. The neck fitting on this has a hole for a screw, but it fits tightly enough to not need it. (at least on this factory doll, I don't have a genuine Blythe yet)

I added a second "neck ball" that is slightly larger than the original one I uploaded. If you print the +.15 one and find it to be a little loose, print the +.2 one instead and it should give a nice tight fit.

Prusa

i3 MK3 MMU 2

No

No

.15

15%