The Cokin Creative Filter System consists of a rectangular plastic filter holder with four slots (one for Cokin rotating filters and three for rectangular ones), a variety of optional adapter rings which click into place and rotate, and many optical resin filters.
There are two Cokin sizes, "A" & "P". The "A" series is adequate for 35mm cameras and camcorders, and fits filter sizes from 36-62mm. The "P" series covers diameters from 48-82mm and is generally preferred for everything, particularly wide angle lenses. Over 100 filters and a wide range of accessories are available for each system, i.e. modular lens hoods, lens caps, and storage boxes.
"A" Series Filter Holder
55mm Adapter Ring
Cokin "A" Series - Filter Holder, 55mm Adapter Ring