The Main Types of Thread

Machining threads main methods are turning, milling, tapping, threading, grinding and thread rolling.

Thread inclued five elements: thread form, nominal diameter, number of threads, pitch (or lead), direction of turning. Same five elements of the internal thread and external thread can be screwed together.

1. Thread form: Pass through the thread axis section area, the thread outline shape is called thread form. There are triangles, trapezoids, serrated, arcs and rectangles, etc.
2. Nominal diameter: The thread has major diameter( d, D), pitch diameter (d2, D2) and minor diameter (d1, D1). Show the thread is used nominal diameter, nominal diameter representing thread size diameter. Plain thread nominal diameter is major diameter.
3. Number of threads: along a helix formed thread is called a single thread, along axial direction equally spaced distribution, two or more helix formed thread is called multiple thread.
4. Pitch and lead: pitch (p) is the axial distance between two adjacent threads on the pitch line.Lead (ph) is in the thread or worm, axial distance from adjacent corresponding point on the same helix. For single thread, lead = pitch; For multiple thread, lead = pitch × number of threads.
5. Direction of turning: clockwise screw thread is called right hand thread; Counterclockwise screw threads is called left hand thread.

The thread is divided into connection thread and transmission thread.

Connection thread:

1. Triangle thread: also called plain thread, is the most commonly used connection thread, self-locking performance is good, high strength.
2. Straight thread: often used in water, gas, lubrication and cable piping systems.
3. Taper pipe thread: often used in high pressure, high temperature, or high sealing requirements of the pipeline system.

Transmission thread:

1. Rectangular thread: has the highest transmission efficiency, but the thread root is weak and easy to wear out, which has been gradually replaced by trapezoidal thread.
2. Trapezoidal thread: good workmanship, high thread root strength, is the most commonly used transmission thread.
3. Sawtooth thread: both rectangular thread and trapezoidal thread characteristics, but only one-way drive.