Elements of thread

Elements of thread 
The thread includes five elements: profile, nominal diameter, number of lines, pitch (or lead), and direction of rotation. cnc machining part
1. tooth type
The profile shape of the thread is called the profile shape on the section area passing through the thread axis. There are triangle, trapezoid, zigzag, circular arc and rectangle.
Thread profile comparison:

 

 
2. Diameter

There are major diameter (D, d), medium diameter (D2, D2), minor diameter (D1, D1) in the thread. The nominal diameter is the diameter representing the thread size.

The nominal diameter of a common thread is the major diameter. cnc turning part

 

 
External thread (left) internal thread (right) 

 
3. line number
The thread formed along one helix is called single line thread, and the thread formed by two or more helixes equally distributed along the axial direction is called multi line thread.
Single

thread (left) double thread (right) anodizing aluminum part

4. Pitch and lead
Pitch (P) is the axial distance between two corresponding points on the pitch diameter line of two adjacent teeth.
Lead (PH) is the axial distance between the two adjacent teeth on the same helix and the corresponding two points on the pitch diameter line.
For single thread, lead = pitch; for multi thread, lead = pitch × number of threads.

 
5. rotation direction
The thread that is screwed in when rotating clockwise is called right-hand thread;
The thread that is screwed in when rotating counterclockwise is called left-hand thread.

 

Left hand thread right hand thread