"Pete C." writes:

What, if anything, should the marking on the head, "Y D" tell me about
the grade of the screw?

Ying Dong noodle factory perhaps?

Not the kind of technically informed answer I was looking for.

If it's safety critical just go spend the $20 and buy new grade 9
hardware from a reliable source.

Well, bought from a dedicated industrial hardware distributor, not from
the local hardware store or Walmart.

Good thought, though.

--
Mike Spencer Nova Scotia, Canada