Universal Professional 77MM Lens Hood is primarily designed to prevent unwanted stray light (flare) from entering the lens by extending and shading the end of the lens. In addition, since the end of the lens is extended, you also get the added benefit of some extra protection from accidental impact. Screw-mount lens hoods, such as this 77mm, are designed to screw right into your lens or filter. Rear locking ring allows the user to rotate the hood in 360°direction.

Lens hood is compatible with the following lenses + many other lenses that have a 72mm thread:
Canon
EF 17-40mm f/4L
EF-S 17-55mm
EF 24-70mm f/4L
EF 24-105mm
EF 28-300mm
EF 70-200mm f/2.8L
70-200 2.8 IS USM
EF 100-400mm
EF 24mm f/1.4L
EF 300mm f/4L
EF 400mm f/5.6L
EF-S 10-22mm
EF 16-35mm f/4L
EF 24-105mm f/4L IS II USM Lens
24-70mm f/4L Lens