How is the factory jack mounted?

RedFish said

The jack pictured in a blue trunk is same as 67 fish. It will hook on the bumper but just barely. In my opinion it is for show only and absolutely not to be used. I have a small jack of different type tied to the properly placed OEM jack with bungee cords.

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It looks like it would just barely get a hold on the bumper, and there are certainly better ways to jack the car up.
BUT, I used those jacks for years and years when I was a kid and they always held and did the job.
It looks like a tiny little edge that catches the bumper but the downforce on that little hooked area is pretty solid, and I have shaken the heck out of some of the cars while up on the jack and the thing never budged.