Fan Guards and Filters CUI Devices Fan Guards and Filters are designed to complement CUI Devices' standard DC fan frame sizes of 40mm, 50mm, 60mm, 70mm, 80mm, 92mm, and 120mm. A 35mm fan guard is also available. These components are available in metal or plastic and in a variety of designs. The metal fan guards feature a steel wire frame with nickel chrome plating, while the plastic fan guards are designed with a black PA-707 material. The fan filters are housed in black PA-707 plastic and use 30PPI polyurethane foam to help keep particulate ingress away from internal components. All of the plastic housing meets UL 94 HB flammability standards, and all of these CUI Devices models are RoHS compliant.