In the far-off past when radio was nearly all Morse code (what's that Fessenden fellow on about?), everybody keyed fairly high currents in the primary side of big transmitters, especially spark rigs. Commercial stations used big, purpose-built keys or keying relays. Hams....improvised.
This example was found on Etsy. "Dime keys" are often fakes; this one, the key's an older type, the solder looks like the old-time stuff, the dimes are sure-enough silver and the knob bears an "Aug 3, 1920" patent date; a little late but not too late. So it's probably the real deal.