Hydrogen embrittlement fracture of bolts is a common form of failure. Because hydrogen embrittlement fracture is delayed and concealed, the damage it brings is much greater than the damage caused by other fractures. Since this century, hydrogen embrittlement fractures of alloy steel bolts have been commonplace, seriously hindering the normal development order of aerospace models, and have reached the level of "talking about hydrogen discoloration". In order to enable more scientific and technical personnel to understand the mechanism of hydrogen embrittlement, grasp the law of hydrogen embrittlement of bolts, and effectively prevent the occurrence of hydrogen embrittlement of bolts, the results of these studies are now written and introduced for readers' reference.

Pan-head screws and round-head screws are often difficult to distinguish because of their similar appearances. In fact, different screw head types have different uses. Below we introduce the difference between round head screws and pan head screws, I hope it will be helpful to everyone.