Screw and bolt head type and features

The head shape of bolts and screws can be divided into six categories: hexagonal heads, double hexagon heads, spline heads, pan heads, countersunk heads and other head shapes. Except for the sinking head, it belongs to the convex head. The tensile strength of the stud bolt is mainly determined by the strength of the thread. The strength of the countersunk bolt depends mainly on the strength of the head.

Hex head bolt features

The heads of hexagonal head bolts and cylindrical head bolts are often made with locking wire holes. After the bolt is tightened, the wire is passed through the lock wire hole of the bolt, and a group of bolts are connected in series to restrict each other, thereby playing a common role of preventing loosening. Alternatively, the lock wire can be used for sealing to prevent detachment.

Countersunk head screw features

The countersunk head can be divided into (flat) countersunk heads and semi-sunk heads. There are generally three types of countersunk heads: 900, 1000 and 1200. In the Russian standard system, it is customary to use 900 and 1200 countersunk heads. The 1200 countersunk head is mainly used for thin-walled structures (such as thin skins), but because the thickness of the head is thin, the depth of the screwing groove is not well controlled, the groove is too shallow, the screwing performance is too poor, and it is easy to “slip” when assembling and removing bolts. "The groove is too deep, which will weaken the strength of the nail head and make it easy to turn around. In the ISO/TC2 standard system, there are only 900 countersunk heads, while in the ISO/TC20/SC4 standard system, there are only 1000 countersunk heads and 1000 small countersunk heads. The small countersunk head refers to the type of reduced head height, which is used for the thin-wall structure of aerospace vehicles. Due to the characteristics of the countersunk bolt structure, the head strength is generally lower than the screw strength or the thread strength, and the countersunk bolt is subjected to tensile failure. During the test, the bolt head is always destroyed first.

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Label: Screw and bolt head type and features

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