Nikon made Rangefinder 35mm cameras that were copies of Contax designs. Therefore, those cameras used Contax mount lenses.
The F Mount
In 1957 Nikon decided to produce 35mm slr cameras in order to have a system which could easily support long telephoto lenses. They modified the Contax rangefinder design and came up with the Nikon F. The mount was called the Nikon F Mount. That basic F Mount design is still being used today in Nikon's D-SLR's. Nikon F cameras, and Nikkormats as well, used meters that were linked to the aperture setting on the lens by a pin which connected to the lens by way of a little prong. In order for the meter to know which f stop was being used, the user needed to mount the lens at f5.6 then turn the aperture ring to its smallest setting, then back to its largest setting. This was called the Nikon swing. The meter knew the aperture setting by the position of the pin. These lenses are called Non-Ai. They will not mount on camera bodies made for Ai lenses or newer.
Nikon F (Non Ai)
In 1977 Nikon modified the F Mount. It was no longer necessary to do the 'Nikon Swing' in order for the camera's meter to know what the aperture setting was. There was now a notch cut into the base of the lens which would meet with a lever on the camera body that was connected to the meter. It was no longer necessary to catch a pin with the lens fork anymore. They called this Aperture Indexing or Ai. Nikon left the fork on the lens in case users wanted to mount the new style Ai lenses on their Nikon F bodies. They modified the forks by cutting holes to allow light to hit the base of lens. This made viewing a second set of aperture numbers much easier.
In order to make pre-Ai lenses usable on Ai bodies, Nikon offered an Ai service. Factory Ai'd lenses had their old mounts replaced and the prong changed. Factory Ai'd lenses are considered unaltered by collectors and Nikon.
It is possible to Ai convert a lens when you do not have a proper replacement mount. Ir requires cutting a gap out of the rim of the mount, changing the prong and gluing an aperture strip onto the lens under the prong. These 3rd party modifications may work but they are frowned upon by collectors and Nikon. I see alot of ruined lenses that were Ai'd by scam artists or misguided amateurs. Some are done well but they are rare. If you plan to have a lens Ai'd, PLEASE look at examples of the repairman's work before you ruin your lens.
In 1981, Nikon modified the mount again. With an Ai-S lens atteched, the camera could control the aperture by itself. This made shutter priority and program exposure possible. Ai-S mounts have a thinner collar surounding the rear lens element. Ai-s lenses have their highest aperture number colored orange. There is also a notch cut into the mount which tells Ai-S capable cameras that it's an Ai-S lens. In 1983 Nikon made a modification which allowed camera and lens to communicate with a CPU.
Also, in 1983, Nikon introduced autofocus on the F3 AF. They had been working on an autofocus lens since 1971. With the FS AF they introduced two lenses that had internal motors. In 1986 they decided to mass produce autofocus cameras. They introduced the N2020 which used the Nikkor AF mount. These lenses do not have internal motors. The motors are located in the camera bodies. A small screw head at the base of the lens is turned by the camera motor, and this screw head turns the focus ring. Nikkor Af lenses will mount on earlier manual focus camera bodies but will not Autofocus. On early F mount cameras you will need to use stop down metering because the lens does not have a prong. You may add a prong if you so desire.
In 1996, the CPU in AF lenses was modified to relay focus distance infornation to the cameras metering system. This was primarlily done to improve flash exposure. The mount did not change externally, except for the use of plastics. Look for the 'D' written after the lens designation.
In 2000, Nikon did away with the aperture ring on autofocus lenses. These were 'G' lenses. Since they do not have an aperture ring they can not be used on Nikon cameras without a CPU. Look for the 'G' after the lens designation.
Nikkor AF-I & AF-S
These lenses have internal motors. There is no screw drive in the lens mount. They are also 'G' lenses because they don't have an aperture ring. Look for the AF-S on the lens designation.
Nikkor AF-S 'G'
The DX mount is a modified F mount which fits Nikon sub frame Digital slr's. It is basically a smaller AF-S mount.
Other Nikon Mounts
Nikonos and Nikon RS
Nikonos cameras were based on Calypso cameras. Nikon bought the rights to the design and produced the Nikonos I. It was a manual focus underwater camera. In 1992, Nikon introduced the RS. The RS used a variant of the F mount. They added an outer bayonet ring for waterproofing purposes. It was an autofocus underwater camera.
Introduced in 2011, this mount is used on Nikon CX format mirrorless camera bodies.
Nikon 1 Mirrorless
I'm sure Nikon would like to forget that APS cameras were ever made but I won't forget. APS cameras were an attempt to broaden the market by getting you to buy a new camera system. Nikon, Fuji, Minolta and Kodak got together and created the system. Each company contributed to the cause. Nikon, Minolta and Kodak made cameras and Fuji made minilab modifications. As a salesman I begged my customers not to buy an APS camera. Nikon made Pronea cameras for the APS system. They developed a new lens mount for it. Here it is.
Nikon IX Pronea