A hash hole is a small cavity or depression in a piece of wood or metal that typically occurs due to natural defects, manufacturing processes, or damage. In woodworking, hash holes may appear as knots or voids where resin or sap has gathered, often affecting the material’s structural integrity and aesthetic. In metalworking, hash holes can refer to surface imperfections caused by corrosion, pitting, or machining errors. These holes may require filling, reinforcement, or other treatment depending on their size and impact on the overall material performance.