Rotating knob retractable nib with internal helical grooves

My only knowledge of this is from David Nishimura’s website. Rather than try to explain, I refer you to his excellent explanation and pictures. The difference is that with extension or retraction of the nib, the nib will be seen to rotate. On the other version, the nib does not rotate as it extends or retracts.

Specifically here:

https://vintagepens.com/Waterman_safeties.shtml

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