SpeakON female connector 4 solder contacts of the STX series that I used for the manufacture of cables for connecting high power amps to speakers. Very solid, it consists almost entirely of metal.
I use for the cable 2 and x 4 mm ² to 16 mm outside diameter. Neutrik says it supports up to 6 mm ², I have not tried it and it should not be obvious.
The connector connects and disconnects easily, no false contacts.
Level locking, it is best to Neutrik Speakon (better than the SPX series).
Price accordingly, but "The price is forgotten, the quality remains! "