Some motors come with CW (clockwise) and CCW (counter clockwise) prop shaft threads. The difference is the thread orientation on the prop shaft are the opposite. That means one prop nut can be fastened by rotating clockwise, and the other prop nuts needs to be rotated the other direction.
They call this ‘Self locking’, because on a quadcopter we have 2 motors spinning CW direction and the other two spinning CCW. As the motors are spinning, the prop nuts automatically tighten themselves and doesn’t come loose.
However to many people like myself, I get confused very often especially when you need to get prop nuts replacement. So which one is CW and which one is CCW? Also when you are ordering nuts, they are not categorized as CW or CCW, but rather right handed and left handed thread.
Identify CW and CCW Motors
So basically, if you can fasten the prop nuts clockwise, then you have a CW motor or prop shaft.
If you have CW motor, get the Right handed thread nut (standard thread).
For CCW motors, go for left hand thread nuts (reverse thread)
Please don’t mix up motor direction with propeller direction. Motor direction should be opposite to propeller direction when installing. E.g. CW motors should be installed for CCW propeller rotation, follow this diagram.
Basically the left / right hand thread follows the right hand rule.