B+W 39mm Circular Polarizer with Multi-Resistant Coating 66-1069183 This filter uses our standard B+W F-Pro filter mount, which has a front accessory thread and is made of brass. MRC by B+W is not only an extraordinarily effective multiple layer coating, it is also harder than glass, so that it protects filters from scratches, and it is also water and dirt repellent, thus facilitating filter maintenance. Manufactured from Water-White Schott Glass