This left-side moldboard breast is the forward-facing curved plate on the plow body that lifts and inverts the soil slice. It bolts to the frog and the moldboard extension; the two mounting holes are spaced to match the body pattern. The matching bolts are M10x30 and M12x35. A worn or cracked breast causes incomplete soil inversion and increased draft force. The manufacturer machines this component to the original curvature profile so the soil flow across the full moldboard surface remains uniform. On reinstall, use the specified bolt torque and check that the breast seats flush against the frog.