JJC RR Series Reverse Rings are threaded on one side to fit the filter thread of your lens. The other side has a mount like your camera lens. Screw the adapter into your lens' filter thread, turn the lens around and bayonet it into the camera body. This greatly increases the macro reproduction range capabilities.
Nikon D3000 with JJC RR 52mm Reverse Ring Mounted.
Nikon AF 50mm F/1.8 Lens Reverse Mounted on Nikon D3000 DSLR.
Nikon AFS 18-55mm F3.5-5.6G lens Reverse Mounted on Nikon D3000 DSLR