Made for U.S. Shipping Board in 1920 by MACH'Y DIV. NAVY YARD Boston.
These large keys used .625" diameter silver contacts to handle
the high currents of spark transmitters.
The brass ring around the lower contact is a "cooling ring."
The base is made of hard rubber.
Originally the SE68A is a "leg-key,"it had long threaded rods on the bottom of the key base
that allowed direct mounting to a table with connections made to the rods from under the table.
(The SE68A was later sold as surplus to hams and are advertised in
the back section of the 1937 ARRL Handbook for $7.50.)