What is the difference between single thread and double thread?

The thread formed along a helical line is called a single thread, and the thread formed by two or more helical lines equally spaced along the axial direction is called a multi-thread thread.

The following figure shows the diagrams of single thread and double thread.

Because of its small helix angle (not easy to slide), single-thread thread has a large friction force formed by the screw and nut (with self-locking ability). It is used for thread locking, such as screws and nuts for fixing ceiling fans, and gas bottles. Fixed connection between joints and parts in mechanical equipment, etc。

The multi-threaded thread is used to transfer power and movement due to its large thread lift angle (easy to slide), and the friction formed by the screw and nut screwing is small, which is used to transmit power and movement, such as a jack used to raise the wheel for maintenance and used to clamp the workpiece. Bench vices for fitter processing and lathe screws for thread processing, etc.

The lead of the multi-threaded thread is larger, and the lead of the double-threaded thread with the same pitch is twice that of the single threaded thread, but the self-locking ability decreases when the thread lead is larger. Simply put, the overall force is perpendicular to the normal direction of the thread. After acting on the surface of the thread, it is broken down into axial and radial component forces. A thread with a large lead has a small axial force. Therefore, the transmission mechanism is mostly multi-threaded. The bolts used for locking are mostly single-headed, with large axial force and high friction, which can be self-locked, and the nut will not fall off by itself.

Refer to different

1. Single thread: It is a mechanical material, and there is only one thread with a spiral groove on the cylinder.

2. Multi-threaded thread: A thread formed by two or more axially equally spaced spiral threads.

The processing difficulty is different

1. Single thread: CNC machine tool is easy to process.

2. Multi-threaded thread: It is difficult for the finish on both sides of the tooth profile to meet the drawing requirements, especially for the multi-threaded thread with large pitch and large worm modulus, it is more difficult to guarantee the accuracy requirements on the CNC lathe.

The role is different

1. Single thread: mostly used in slow mechanisms.

2. Multi-threaded thread: The spirals are equally spaced along the axial direction. Solving the problem of equidistant distribution is called splitting (line dividing). The size of the equidistant error affects the meshing accuracy and service life of the thread. The multi-threaded thread can move several times the pitch every time it rotates once, and it is mostly used in fast mechanisms.