The Novoflex NIKLEI-K Lens Mount Adapter is the required adapter ring to connect a Nikon AI type camera body to the Novoflex Balpro series bellows system. This adapter ring has the Leica M39 screw mount at the other end, but you will still need the Novoflex #APRO (B&H #NOA35) to go from this NIKLEI-K ring to the bellows itself.
Note:
Although the lens will fit physically, access to various lens and camera functions are not guaranteed. No electronic communication is possible between the camera and the lens.