Professional Tulip 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 55mm, are designed to screw right into your lens or filter. Rear locking ring allows the user to rotate the hood in 360°direction.

Why should you use lens hoods?
Essentially, a lens hood acts to block out light that the lens shouldn't be receiving, which can contribute to aberrations such as flare, particularly when shooting towards the light. Wide angle lenses, due to their expanded field of view, are naturally prone to gathering stray light, though the reduced field of view on standard and telephoto lenses means that for accuracy, the use of lens hoods is just as important.