Mild Carbon Steel Flat Ground Stock 4.81" x 22-3/4" x 24-1/8" 490Lbs

 Mild steel. No grade stamp on this piece.  
Thickness:  4.814"  (Should be within +/- .005")
Width:  22-3/4"
Length:  24-1/8"  This is the outer length and width, the other specific measurements are marked in one of the photos.
Weight:  490 Lbs