Rear lens cap deep 23mm for rangefinder Nikon S wide anger lenses for example, 28mm f/3.5, 35mm f/1.8 and 35mm f/2.5. Zeiss Contax rangefinder camera lenses  postwar Biogon 35mm f/2.8, Biogon 21mm f/4.5. Russia Kiev camera wide anger lenses. See the picture.

It's a generic plastic cap not made by Nikon. 

Good luck and thank you for bidding.