The 
NUPROL NP 40mm Sunshade
 is an alloy scope accessory designed to reduce lens glare, improve image clarity, and offer minor physical protection for airsoft optics with a 40mm objective lens diameter.
 
Product Details
Function: The primary purpose is to shade the objective lens, which reduces the amount of excess light entering the optic, thereby improving clarity and minimising sun glare or reflections. It can also help prevent the sun's reflection from giving away your position during airsoft games.
Material: The sunshade is constructed from a durable alloy.
Compatibility: It is designed to screw directly onto scopes with a 40mm objective lens diameter and is threaded at both ends, allowing multiple sunshades to be used in sequence or to attach a NUPROL Killflash of the same diameter.
Protection: While its main function is glare reduction, it offers some protection from incoming BBs by reducing the target field for the enemy on your optic. For complete protection against direct BB hits, a NUPROL Killflash or Lens Shield is recommended.
Aesthetics: According to some descriptions, the sunshade adds a "chunky" look to the scope, which some users find appealing.