David Harmon wrote:
Is there any particular plug/socket type connector that is an accepted
standard or most prevalent kind for connecting a CW key to a radio?


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Most (older) radios have a 6.3 mm (1/4 inch) telephone jack socket
either 2 lead or 3 lead (stereo model) when having a built-in keyer.
I also have seen radios with for the Key a RCA audio socket .

Frank GM0CSZ / KN6WH