The Lens Mount Cap from OP/TECH USA is sure to be a hit with both amateur and pro photographers. Its no ordinary cap the benefits and versatility are sure to please. Its designed with an O-ring seal which creates a positive contact with the full perimeter of the lens mount area to really lock out dust and moisture. It also offers a tighter friction fit over traditional caps that come with the lens so that it provides better protection to the lens mount area. This ensures that the Lens Mount Cap is securely held in place while in storage or transit.