The 67mm Mounting Ring from Vu Filters works in conjunction with the VFH75 Holder, and gives many options of filters to use with your lens. The Mounting Ring screws to the front threads of the lens and the holder slides onto the mounting ring. There are two thumb screws that tighten and prevent the holder from falling off the mounting ring.
Square or rectangular filters can be used at the same time with the Vu Sion Slim Circular polarizing filter, because it screws onto the Mounting Ring and rotates independently inside the holder from the rest of the filters.