Tow Hook comparison-with #'s-what is it?

[mkmiller1]

Here is a pic of a hook that I had to cut off the front (homemade) bumper of my '71K10. I've put it beside a rear hook off a bus to give an idea of what size it is. The smaller hook has some #'s in the curved area on the hook, they are: 1257-L also has some unreadable #'s below those that appear to be: 333 AZ (not sure on these except for the "Z"). As you can see they have the same curve as the bus ones but are smaller. ANY IDEAS?
Thanks,
Matthew