A completely standard run of the mill quarter inch (that’s the “big” size) Mono Audio Plug, metal with springy strain relief.
This size of plug is 1/4”, which is 6.35mm, but sometimes also called 6.5mm
Standard solder tabs under the cover for ground and signal.
Can't say much more about this, not really very exciting, but if you need one, you need one.
Commonly used with “big plug” mono microphones and .electric guitars I think also are commonly mono quarter inch (but I’m no guitar guy).
Be sure to see my other audio plugs and sockets listings
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