It has a #2 diopter - which means that when it is attached to ANY lens, and the lens is focused at infinity, the point of focus will be 500mm (20").  Adjusting the lens to focus closer, and the lens can focus much closer than normal -- as close as 8 inches or more.

The Nikon close-up lenses are different from most close-up lenses, such as Vivitar, because they are made with TWO glass elements to reduce chromatic aberrations and color fringing.  In addition, they are multi-coated to reduce glare.

It can be used alone or added to a macro lens or tele-converter to get extra magnification.  Results are best when stopped down.

This one looks unused and comes with a hard, clear case.