Bolts and screws are the most used and the largest batch of external thread fasteners, and the most common processing methods are generally rolling and cutting.

The most commonly used cutting methods are turning, milling and wire bushing, among which turning thread is the easiest to achieve and has higher efficiency. It is also suitable for the processing of fasteners of various materials, specifications and precision.

However, because cutting is a type of thread obtained by removing the excess of the material, the metal flow line is cut during machining (Figure 1), the resulting thread is usually not very strong and has a limited fatigue life. Therefore, this method is not suitable for large batch and high performance requirements of aerospace external thread fasteners.

The most common thread processing method for aerospace bolts and screws is rolling, which is widely used in high strength fasteners. In the relevant aerospace fastener standards, high strength bolts are generally required to roll the thread.

The aim is to redistribute the metal material along the threaded tooth profile so that the metal streamline is not cut off and has maximum density at the base of the tooth, so that the tensile strength and fatigue fracture resistance of threaded fasteners are greatly improved.

At the same time, rolling thread is also one of the most efficient methods in thread machining. Therefore, in the actual production, rolling thread processing is the most widely used.

Rolling thread is a cold working method that causes plastic deformation of metal to form thread. It can roll the diameter of the external thread, with high production efficiency, fine thread surface roughness, high thread strength and surface hardness, can fully ensure the mechanical properties of parts, so it is the fastener and all mechanical industry in the most widely used thread processing method.