How does the joint of BJD work?

The joint of BJD is made from the ball structure and connected with TPU coated wire rope, so as to keep the adjustability of the doll.

BJDGuide — Single Jointed vs Double Jointed

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Expert Guide: Signs Your BJD Needs a Tune-Up

Double Hip Joint

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BJDGuide — Single Jointed vs Double Jointed

ArtStation - BJD movable joint doll girl Lainey ball joint doll

How to sculpt joints for ball-jointed dolls? — Nymphai Dolls

File:Elbow and wrist joint of male ball-jointed doll.jpg - Wikipedia

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BJDGuide — Single Jointed vs Double Jointed

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