The Haida Magnetic Step-up Ring attaches directly to your lens by screwing into the front threads and allows for filters and accessories in the Haida magnetic series to attach magnetically to the outer side of the ring allowing you to change filters without having to unscrew them from your lensWith a step-up ring the first size listed in millimeters is the size that you will want to attach to your lens with the larger millimeter size the size of the filter or accessory that you will be able to "step up" to