Mill Certificate vs. Design Yield Strength Structural
#0183;#32;A mill certificate is tied to a specific quot;heatquot; or run of steel production. Using rebar as an example (all steel production works in a similar way), one mill might produce a ASTM A615 Grade 60 bar which yields at 61 ksi, while another may produce a bar meeting the same spec which yields at 77 ksi.