Shrewd Lense Housing Retainer Ring Optum Series Scopes Black. This housing fits any lens that is 1.75" in diameter and at least .08" thick. Made from aluminum and anodized for durability. Once a lens is installed the two parts should be locked together using a thread locker. Allows installation of a sunshade on the target side of the lens. Fits both 40mm and 35mm Optum scopes. Specifications for Shrewd Lense Housing Retainer Ring Optum Series Scopes: Manufacturer: Shrewd Color: Black Package Contents: Shrewd Lense Housing Retainer Ring Optum Series Scopes Shrewd SMLHOPTUM: Lense Housing Retainer Ring Optum Series Scopes Black