Page "Circular polarization" Paragraph 22

When using this convention, in contrast to the other convention, the defined handedness of the wave matches the handedness of the screw type nature of the field in space.

Specifically, if one freezes a right-handed wave in time, when one curls the fingers of one ’ s right hand around the helix, the thumb will point in the direction which the helix progresses given that sense of rotation.

Note that it is the nature of all screws and helices that it does not matter in which direction you point your thumb when determining its handedness.