This is a HB-55 hood Adapter for 77mm ring size lens such as Nikkor 85mm f/1.4 D that enables you to transform a 77mm threaded lens into a Quick release hood lens type.
No more hassle using old style threaded hood lens anymore.
 
It also has 77mm front thread for you to install your favorite filter.
 
Please check 2 Youtube videos for the demonstration by searching the titles below:
HB-55 hood Adaptor Nikkor 85mm f/1.4 D #1
HB-55 hood Adaptor Nikkor 85mm f/1.4 D #2