Threads are everywhere at work. Threads types are variable and it is hard to tell the differences if you do not know their features. All kinds of threads can be recognized at a glance should be will be of some help to your work.
Firstly, let us learn about the basic parameters of threads.
In the above image:
"d" stands for the nominal diameter of thread.
"d1" often used in strength calculations.
"d2" often used in geometric calculations.
"α" is an angle between the two sides of a threaded tooth in an axial section.
"h" is the distance between the top of the tooth and the bottom of the tooth perpendicular to the axis.
"P" stands for the axial distance between the corresponding points on the adjacent two threaded teeth on the meridian line.
"n" stands for the number of spirals of a thread.
"S" stands for the axial distance to travel along the same helix on the thread, S=nP.
"φ" stands for the Angle between the tangent line of a helix and the plane perpendicular to the axis of the thread.
Then, let's learn more about some common threads.
International Metric Thread
The thread Angle is 60 degrees, and the specification is expressed in M
American Standard Thread
The top and root of the thread are flat, with good strength.The thread Angle is also 60 degrees, and the specification is in the number of teeth per inch. The notation is 1/2-10NC.(1/2: outer diameter;10: teeth per inch; for short NC ).
Made by the United States, the United Kingdom, Canada, for the commonly used British thread.The thread Angle is also 60 degrees, and the specification is in the number of teeth per inch.The thread can be divided into coarse teeth (UNC);Fine thread (UNF);Extra fine teeth (UNEF).The notation is 1/2-10UNC.(1/2: outer diameter;10: teeth per inch;UNC code)
Sharp V Thread
Top and root are pointed, weak strength and infrequently used.The thread Angle is 60 degrees.