I'm surprised there isn't a standard connector by now. See image below of a Mk4A helmet. When introducing this, I wanted to use a 9 (I think) pin "snatch" connector, used by US Apaches. This met the UK spec for pull weight on emergency egress, which is about 8lbs.
I was told "No" in no uncertain terms by OR so had to go for what you see. They are staggered so one pulls before the other, to meet the 8lb limit. Also, you can perhaps see each is a different diameter, so you cannot mix them up in the dark, and the smaller one has a different sleeve length (the bit furthest from the tip). This was to avoid shorting as you could get this one in the others female socket, but not vice versa. Hope that makes sense.
I seem to recall the UK NATO connector design dates from about 1947, and originals remain in service!
