Joints are used to control bones. There is one joint at each end of a bone.
Joints control bones, and bones control objects (attachments).
Any joint can be nailed. You can move a nailed joint manually,
but it will not move because of IK links when other joints are moved. Nailed
joints are drawn in red.
When you select a joint in trueSpace, the bone controlled by that joint is selected
in Motion Studio.
If you select a bone using the Skeleton Items list,
the joint at the tip of the bone is selected in trueSpace.
The size of a joint is based on the average of the lengths of the bones to which
it is connected. This way, joints used with small bones (in high-detail areas)
will tend to be smaller and joints used with large bones will be larger.