The Nikon HB-40 Lens Hood is a dedicated lens hood for use with the AF-S Zoom Nikkor 24-70mm f/2.8G ED lens.
The petal shape of this lens hood is designed to maximise the prevention of unwanted stray light from entering the lens whilst keeping weight and hood area to the minimum.
It matches the specific focal length of the lens and also provides the additional extra protection for the front element from accidental impact.