Basic terminology in different tools : Bone versus Joint - enimaroah/SB3Utility GitHub Wiki

cf_j_ring04_L is a joint, in Maya. But in Sb3UGS you see only Transforms and Bones.

To make it short, the naming "Bones" in Sb3UGS is wrong. But I will leave it as it is only for traditional reason.

The same scene in Sb3UGS. Huh, where is this leaf joint/bone? (It is a leaf because it has no childs).

Sb3UGS shows only bones of the list in the hierarchy below the SkinnedMeshRenderer node in the Object Tree. And it shows bones from its joint position growing bigger against its root which is the parent bone.

cf_j_ring03_L is not a leaf bone, but the last in the chain which the body has weights for. The meaning of this? When you rotate cf_j_ring04_L - the real leaf - no vertex will change its position. The body mesh has no weights for it. You could delete the animation track and the Transform in the hierarchy and the animation would look the same.

Not so, if you would make cf_j_ring04_L a bone with weights for it in the tip of that ring finger. Then the animation track with the same name would influence the finger tip when the animation is played.

In Blender the Joint position is the position of the bone's "Head".