Bolt detection is divided into manual and machine. Manual is the original and common way of consistent detection. In order to reduce the outflow of defective products as much as possible, the general production enterprise personnel visually inspect the packaged or delivered products to eliminate the defective products (including tooth injury, mixing, rust, etc.).

另一種方式為機器全自動檢測，主要是磁粉探傷。磁粉探傷是利用螺栓缺陷處的漏磁場與磁粉的相互作用，針對螺栓可能存在的缺陷（如裂紋，夾渣，混料等）磁導率和鋼鐵磁導率的差異，磁化后這些材料不連續(xù)處的磁場將發(fā)生崎變，形成部分磁通泄漏處工件表面產(chǎn)生了漏磁場。

Another way is automatic machine testing, mainly magnetic particle testing. Magnetic particle inspection is based on the interaction of magnetic flux leakage field and magnetic powder at the defect of bolt. In view of the difference between the permeability of the defect (such as crack, slag inclusion, mixture, etc.) and the permeability of steel, the magnetic field at the discontinuity of these materials will change after magnetization, forming part of the magnetic flux leakage on the workpiece surface.

從而吸引磁粉形成缺陷處的磁粉堆積——磁痕，在適當?shù)墓庹諚l件下，顯現(xiàn)出缺陷位置和形狀，對這些磁粉的堆積加以觀察和解釋，已達到剔除不好品的目的

So as to attract the magnetic powder to form the magnetic powder accumulation at the defect, the magnetic mark, and show the position and shape of the defect under the appropriate light conditions. By observing and explaining the accumulation of these magnetic powder, the purpose of eliminating the bad products has been achieved