What you are viewing is a Mennon Portable 77mm White Balance Lens Filter Cap, which is a professional lens filter cap for all 77mm size lens well, and can be used for white balance measurement and as a lens filter cap!
The 77mm lens cap keeps a spare cap in your gear bag for the inevitable lost lens cap, too! Pinch the sides of the white balance lens cap and snap it into place-it fits securely and your lenses are covered. Whether your hand are tender or coarse, the lens filter cap will take on or off easily when you using the hood. Made of high quality material, the lens filter cap is durable and reliable for long time use.
Give your camera best care, you should get the white balance lens filter cap.