What Is a Threaded Rod?

Threaded fasteners are mechanical parts with internal or external threads. They are generally used as fasteners to facilitate the assembly of multiple components. The most common threaded fasteners are screws, nuts and bolts. However, there are other threaded fasteners, such as cage nuts, threaded inserts, threaded rods, etc. ^[1] .

Threaded fasteners are used on almost all mechanical equipment. Therefore, threaded connection technology is one of the most important technologies to ensure the reliability of mechanical systems. Due to frequent use, threaded fasteners have become one of the most standardized parts. In general standards such as ISO and JIS, bolts, nuts, and washers have been provided according to their size (

Threaded connection is a widely used detachable fixed connection, which has the advantages of simple structure, reliable connection and convenient assembly and disassembly. The traditional thread detection method is to use a thread gauge for contact or manual measurement with a universal tool microscope. The workload is large, the work efficiency is low, and the measurement results are easily affected by humans.

According to the shape of the plane graphics, the threads can be divided into triangular, rectangular, trapezoidal and zigzag threads. According to the winding direction of the spiral, it can be divided into left-handed thread and right-handed thread. It is stipulated that when the thread is upright, the helix is raised to the right to the right-handed thread and to the left is left-handed. Right-handed threads are generally used in mechanical manufacturing, and left-handed threads are used only when special requirements are required. According to the number of spirals, it can be divided into single-thread threads and multi-thread threads arranged at equal distances. For manufacturing convenience, the thread generally does not exceed 4 wires ^[2]

Features of threaded connections:

(1) A large axial force can be generated when the threads are tightened;

(2) It can easily achieve self-locking;

(3) small dimensions;

(4) It is simple to manufacture and can maintain high accuracy.

Types of	Features and applications
Bolted	Used to connect two thinner parts. A through hole is opened in the connected member. There is a gap between the rod and the hole of the ordinary bolt, the processing requirements of the through hole are low, the structure is simple, the assembly and disassembly is convenient, and the application is wide. Hinge hole bolts (GB / T 27) often use transitional fits such as H7 / m6, H7 / n6. This connection can accurately fix the relative position of the connected parts. It is suitable for bearing lateral load, but the machining accuracy of the hole is high. Drilling and reaming are often used.
Stud bolt connection	It is used in the case where one of the connected parts is thicker and is not suitable for bolting. The thicker connected parts have lower strength and need to be disassembled frequently. Threaded holes are machined on thick parts, light holes are machined on thin parts, bolts are screwed into the threaded holes, and the thin parts are pressed with nuts. When removing, you only need to unscrew the nuts without removing the studs. Prevents damage to threaded holes in large parts
Screw connection	The bolt (or screw) is directly screwed into the threaded hole of the connected component without a nut. The structure is simpler and more compact than stud bolts. For one of the two connected parts that is thicker, but does not need to be dismantled frequently to avoid damage to the threaded hole
Set screw connection	Use the threaded end screwed into the threaded hole of the part to bear against the surface of the other part or into the recess on the other part to fix the relative position of the two parts. This connection method has a simple structure, and some can change the position of the part in the circumferential or axial direction for adjustment, such as the fixing of an electrical switch knob
Countersunk head screws	It is used for occasions where the strength is not high and the thread diameter is less than 10mm. The head or part of the screw sinks into the connected part. This structure is mostly used in situations that require a flat outer surface, such as an instrument panel
Self-tapping screws	It is used for occasions where the connection strength is not high. But generally, the bottom hole should be made in advance. If self-drilling and self-tapping screws with a drill part are used, no need to prefabricate the bottom hole, used for non-ferrous metals, wood
Wood screw connection	Generally used for the connection of wooden structures. Depending on the hardness of the material and the length of the wood screws, the wooden parts may not be prefabricated or a certain size and depth of prefabricated holes may be made.
Self-tapping locking screw connection	The thread is an arc-shaped triangular interface. The screw is hardened on the surface and can be screwed into a pre-made hole of a metal material to be extruded to form an internal thread. The internal thread formed by extrusion improves the strength by more than 30% than that of cutting. The small tensile strength of the screw is 800 MPa. Self-tapping locking screws have low tightening torque and high locking performance, and have been widely used in household appliances, electrical and automotive industries
Fastener-assembly connection	The washers and external thread fasteners are produced and assembled by a standard factory. China issued 23 production standards for fastener assemblies in 1988. This connector is easy to use, saves time, and is safe and reliable. It is often used in places where fasteners are used to connect tightly, such as terminal blocks in electrical cabinets.

A thread can be defined as a bevel around a cylinder and is equivalent to a bevel. Conversely, the unrolling of the thread is an inclined plane. The self-locking phenomenon means that if the line of action of the total force Q of the main force acting on the object is within the friction angle, no matter how large the force is, there is always a total reaction force R in equilibrium with it and the object remains stationary.

Conversely, if the line of action of the resultant force Q of the main power is outside the friction angle, no matter how small this force is, the object cannot maintain balance. This kind of equilibrium condition that is independent of the force and related to the friction angle is called the self-locking condition. The equilibrium phenomenon of an object under such conditions is called a self-locking phenomenon. The combined force R of the friction angle and the self-locking phenomenon normal reaction force N and friction force F is called the total reaction force supporting the facing object. That is, when the friction force F reaches the maximum value Fmax, the included angle a at this time also reaches the maximum value b, and b is referred to as the friction angle ^[1] .