In Nikon F-mount manual-focus lenses, there are four main designations for lenses that refer to their meter coupling abilities. They are: Non-AI, AI, AI-S, and AI’d. The differences can be noticed by visually inspecting the area on the back of the lens around the lens mount, as well as around the aperture ring.

KEH Camera Blog: Nikon Lenses: Non-AI, AI, AI-S, and AI’d

Very helpful charts to understand Nikon gear. So many different kinds of lenses you need to look at this compatibility chart BEFORE buying used gear. Make sure it works with what you have.

Nikon Lens Compatibility