Bolt inspection can be divided into two types: manual and machine. Artificial detection is the most primitive and commonly used method of consistent detection. In order to minimize the outflow of defective products, general production enterprise personnel inspect the packaged or shipped products visually to eliminate defective products (including tooth injuries, mixing, rust, etc.).

Another method is fully automatic machine testing, mainly magnetic particle testing. Magnetic particle inspection utilizes the interaction between the leakage magnetic field at the bolt defect and the magnetic particle. In response to the difference in magnetic permeability between the bolt's possible defects (such as cracks, slag inclusions, mixed materials, etc.) and the steel's magnetic permeability, the magnetic field at the discontinuous parts of these materials will undergo distortion after magnetization, forming a leakage magnetic field on the surface of the workpiece at some magnetic flux leaks, thereby attracting the magnetic particle to form a magnetic particle accumulation at the defect - magnetic marks. Under appropriate lighting conditions, Showing the location and shape of defects, observing and explaining the accumulation of these magnetic particles has achieved the goal of eliminating defective products.