Type of Bolt Thread
Thread refers to a helical continuous convex part with a specific cross section made on the surface of a cylindrical or conical parent body.
In machining, the thread is cut on a cylindrical shaft (or the surface of the inner hole) with a tool or a grinding wheel. At this time, the workpiece rotates once, and the tool moves a certain distance along the axis of the workpiece. The traces cut on the top are the threads. The threads formed on the outer surface are called external threads. The threads formed on the surface of the inner hole are called internal threads.
By Thread Profile
The thread profile is the geometry of the thread. Base on thread profile, we could sort the thread into these types:
- Ordinary thread
- Pipe thread
- Trapezoidal thread
- Rectangular thread
- Zigzag thread
The first two threads are mainly used for connection, and the last three threads are mainly used for transmission.
| Thread Type | Thread Profile | Features and Application |
|---|---|---|
| Connection thread | Ordinary thread | The tooth profile is an equilateral triangle, and the tooth shape angle α=60°. Under the same nominal diameter, it is divided into coarse thread and fine thread according to the pitch. Fine thread is often used for small parts |
| Connection thread | Non-thread-tight pipe threads | The tooth shape is an isosceles triangle, the tooth shape angle α=55°, and the tooth crest has a large rounded corner Suitable for fittings, plugs, valves and other accessories |
| Connection thread | Thread Sealed Pipe Threads | The tooth shape is an isosceles triangle, the tooth shape angle α=55°, and the tooth crest has a large rounded corner After the threads are screwed together, the tightness of the connection can be ensured by using its own deformation, without any packing, and the sealing is simple Accessories for tubes, fittings, plugs, valves and other screw connections |
| Connection thread | Rectangular thread | The tooth shape is square, and the tooth shape angle α=0°. Its transmission efficiency is higher than other threads, but the root strength is weaker. After the screw pair is worn, the gap is difficult to repair and compensate, and the transmission accuracy is reduced. |
| Transmission thread | Trapezoidal thread | The tooth shape is an isosceles trapezoid, and the tooth shape angle α=30° The internal and external threads are tightly attached in a trapezoidal shape and are not easy to loosen. Compared with the rectangular thread, the transmission efficiency is slightly lower, but the process performance is good, the root strength is high, and the neutrality is good Trapezoidal threads are the most commonly used drive threads |
| Transmission thread | Zigzag thread | The tooth shape is not isosceles trapezoid, the tooth measuring angle of the working surface is 3°, and the flank angle of the non-working surface is 30°. The root of the external thread has a large fillet to reduce stress concentration. It can only be used in threaded connections or screw drives with one-way force, such as screw presses. |
By Thread Direction
According to the thread direction, the thread can be divided into left-handed thread and right-handed thread.
