The HB-60 Bayonet Lens Hood for NIKKOR 70-200mm F/4G ED VR Lens from Nikon is a circular bayonet lens hood designed for the 70-200mm f/4G lens.
Lens hoods are primarily designed to prevent unwanted stray light from entering the lens by extending and shading the end of the lens. In addition, since the end of the lens is extended, you get the added benefit of protection for the lens from accidental impact and the elements.
Dedicated lens hoods, such as the HB-60, are designed to match the specific focal length of the lens for which it was designed. .