MB-600 double rotatable stackable filter stage, for mounting two 6,6''x6,6'' filter frames or smaller. In this stackable filter stage, two filter frames can be placed which can be rotated together. If you want to use two filters which do not need to rotate individually, this filter stage is the most cost-effective solution. The MB-600 double rotatable filter stage is included in the MB-612 kit and the MB-623 kit as well.