The test is divided into manual and machine. Labor is the most primitive and most commonly used consistent detection method. In order to minimize the outflow of defective products, the general production enterprise personnel shall visually inspect the packaged or shipped products to eliminate defective products (badness including tooth injury, mixing, rust, etc.).

Another way is automatic detection of the machine, mainly magnetic particle inspection. Magnetic particle flaw detection is the interaction between the leakage magnetic field and the magnetic powder at the bolt defect, and the magnetic permeability and the magnetic permeability of the steel may be different for the possible defects (such as cracks, slag inclusions, mixing materials, etc.) of the bolt. The magnetic field at the place will be crucible, and a leakage magnetic field is generated on the surface of the workpiece at the part of the magnetic flux leakage, thereby attracting the magnetic powder accumulation at the defect of the magnetic powder--the magnetic mark, under appropriate lighting conditions, showing the defect position and shape, The accumulation of these magnetic powders has been observed and explained, and the purpose of eliminating defective products has been achieved.