What type of plug is this?

What kind of plug is this one in the middle? I'm sure the other two plugs are for mono and video RCA

https://66.media.tumblr.com/56c237dffad535e3ad307d8042c3e4bd/tumblr_pxek77fd8v1u56smdo1_540.jpg
Update: It can't be a 3.5mm jack. For further reference, it's some kind of power plug for an old late 70s VHS camera I found, I'm just trying to find out what type it is
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