This very rare Nikon Macro-Nikkor 12cm (120mm) f/6.3 M39 mount lens is intended to be used with the Nikon Multiphot large format photomacrography microscope. It can be adapted using a focusing helicoil for use on other cameras. It has some minor finish loss on a one of its ridged areas on the barrels exterior. Its aperture is very smooth, and its glass is exceptional with no fungus, haze or separation to its elements. There is no oil on its aperture blades.
See this great writeup of using this lens on a camera: https://redbook-jp.com/redbook-e/macro2/ma12.html
