Various Lens Adapter & Retaining Rings Tiffen 801, 901, 83mm, Series 9, 58mm. Most were used on lenses for 16mm cameras. The Tiffen 901 Retaining Ring is about 85mm and fits Series 9 filters. There are 2 other two rings that are identical (but unlabeled) to the 901. The 58mm-9 is a step adaptor to  Series 9 Filter holder. The Tiffen 83 SS LR 9 is a pressure fit adaptor to use with  Series 9 filters. It is designed to fit the front of a lens with a diameter of about 83mm. The Tiffen 801 Retaining Ring is about 63mm. The last two, S1001-58SR, are Chrosziel Step-down Matte Box Rings (85mm:58mm) allows the 85mm matte box to adapt to a 58mm lens opening. Enjoy!