Western Electric G6 Volume control handset.  Hardwire with new old stock cord and Special Voice Cut Out. 

Black color handset with Chrome trim around the volume control adjustment and a special voice cut out. The Voice Cutout feature can be used so the person on the other line cannot hear your conversation with someone in the room.

New in the box. Has instructions on how to use NOS handset.

These handsets work good for the hard of hearing.