I claim the ornamental design for a metal hardness test block with circular targets connected by alphanumeric grid lines, as shown in the accompanying drawings.
FIG. 1 is an isometric view showing the top, right side, and front of the metal hardness test block with circular targets connected by alphanumeric grid lines.
FIG. 2 is a top plan view of the metal hardness test block circular targets connected by alphanumeric grid lines.
FIG. 3 is a bottom view of the metal hardness test block with circular targets connected by alphanumeric grid lines.
FIG. 4 is a left end view of the metal hardness test block with circular targets connected by alphanumeric grid lines.
FIG. 5 is a right end view of the metal hardness test block with circular targets connected by alphanumeric grid lines.
FIG. 6 is a front view of metal hardness test block with circular targets connected by alphanumeric grid lines; and,
FIG. 7 is a rear view of the metal hardness test block with circular targets connected by alphanumeric grid lines.