Nikon panorama heads
To make panorama (360°) pictures Nikon offered two panorama heads: Nikon AP-1 and Nikon AP-2
Both panorama heads have at their bottom an ISO standard tripod connetor. The AP-2 has an additional water level. All Nikon cameras can be used on both heads. At their side they have indicators for lenses of focal lenghts of 28, 35, 50, 85 and 105 mm. and the degrees. You just put the ring on the focal length in use and after each image shot you click into the next notch.
Note: The codes AP-3 etc. were given to automatic Nikon levels, used in the construction business.