Flat head hex socket cap screws, 1/2" coarse thread, black finish.
What, if anything, should the marking on the head, "Y D" tell me about the grade of the screw?
(Not old bolts; bought new circa 2004.)
Attaching a die insert to the upper die of a 300# air hammer. Potentially dangerous should a bolt break during operation. Looking for max strength fasteners. Wasn't so important for the purpose for which I originally bought the screws.
TIA,