Secured to your trailer

Hey Dave,
I've been known to haul a few.
Why are you NOT using the hook in the pic I have circled?
It is designed to go into that slot with a twist and does not come out like that "S" hook you have in that slot could.
I was just wondering. I haven't been doing long and my tow truck buddy might have told me wrong.
Please advise and
Thanks, John.:glasses7: