Jackbox, Sound-Powered Telephone. Double, submersible to 15 feet with protective cap or mating plug installed. Provides for connection of sound-powered telephone handsets or headsets. A blank plastic engraving strip, white with black core, is provided for the installing activity to mark circuit designations. Connection is made to a Type 9TB4 terminal board mounted in the bottom of the box by use of type L81 terminal lugs. Per NavShips drawing 9000-803-74210 Rev J. Mates with Symbol 2922 plug per 9-S-74211. The NSN for Symbol 2842 is 5935-00-552-6790.