How do you make gameObject face camera on one axis

Unity Engine
,
4

Notes on clamping camera rotation and NOT using .eulerAngles because of gimbal lock:

https://discussions.unity.com/t/838550/2
https://discussions.unity.com/t/838550/4

How to instantly see gimbal lock for yourself:

https://discussions.unity.com/t/854312/2

All about Euler angles and rotations, by StarManta:

https://starmanta.gitbooks.io/unitytipsredux/content/second-question.html