Product Feature:Rolleiflex/Rolleicord Screw Thread Adapter RingThis adapter ring can transfer the unique Bay I, II, III connectors of Rollei? to the universal UV threaded .The universal screw is actually same as an open platform, allowing the player to DIY himself.For example, players can transfer other brands of lenses they like, as well as circular filters and square filter holders, round hoods, and more.As long as the lens of the appropriate diameter can be installed and used.The ring is made of made of aluminum.Friendly Tip:This camera has two lenses,? only one adapter ring can not allow the cover to be more securely covered.Model : BAY I? - M37X0.75 / BAY II? - M39X0.75 / BAY III - M43X0.75,Pls make sure your UV filter thread fit this adapter.Note:Bay2 is not suitable for 3.5E