This is the JJC Reversing Ring Nikon Fit 77mm [JU1277N] JJC RR-AI 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. ...Contact us if you need more help.