The thoracic cage joint and tendons are completed by issue 54 of Hachette Partworks build. However, there is considerable 'wobble' of the tendons. This upgrade allows you to add a plug, which is hidden and removes the wobble, giving a sturdy functional result.
 
You'll receive 2 plugs.
 
All fitting instructions via the 'Fitting' page. You may need to apply glue to secure the parts.