The matte black finished ,brass adapter rings from Heliopan are also called step rings or reducing rings. They offer a simple way of adapting a series of different lens mount sizes or typest to one standard size. This allows using just one set of filters rather than having duplicate filters of different sizes. HELIOPAN offers an extensive selection and range of ring types and sizes. Rings are available from 24×0,5 to 105×1 screw in.
Coupling rings have two male threads to allow screwing two lense together front to front. This will allow macro photography.
Reversal rings, also called retro adapter rings, have male screw threads on each side