Nikkor G-type lenses are ones that do not have a manual aperture control ring. With a few Nikkor-G lens models removal of the rubber ring (mount side) might be necessary to attach the adapter. This can easliy be done without affecting lens function.
Please note that although G-mount lenses fit physically, automatic diaphragm (AE metering), or any other electronic functions are not retained using this adapter. Metering must be done in “stop-down mode” since the lens does not have the ability to control the aperature through the camera body.