The pin is 9mm diameter that pushes into the machine....and I didn't even know it had a name until I just looked it up. My Kemppi machine has hard wired cables which is a bit annoying now I see how easy these are to connect and disconnect!
I had a closer look at some picks on Hyundi website and at least one of the cables seemed to say 16mm squared, so they'll probably be using a 10/25 Dinse connection for those. I'm in the process of adding another Dinse socket my welding machine, so thought if I'd match what this machine uses, I could use the one lead for both in the event I buy one. Thank you for checking that for me.