This joint removes all 3 rotational degrees of freedom. It forces the constraint anchor orientations to be equal. The translational movement is not restricted and both bodies can rotate relative to other bodies as long as both constraint bodies perform the same rotation.

On its own this constraint is not very useful, but combined with constraints that restrict translational movement it creates practical joints. For example, if this constraint is combined with a PointOnLineConstraint, it creates a point-on-line constraint with fixed relative orientations.

One constraint body can be set to the simulation World to create a body that cannot rotate. But in this case it is more efficient and more stable to lock the rotations of the body using RigidBody properties (LockRotationX, LockRotationY and LockRotationZ).

Reference