What to do when you encounter a screw with an unusual pitch and cannot recognize the type of thread? Today, we present an example from one of our readers who faced this issue with a screw having a maximum diameter of 7.75 mm and an internal diameter of 6.75 mm.
How to recognize the type of thread?
If you consider an outer diameter of approximately 7.75 mm and a core diameter of about 6.75 mm in this case, it is likely that it is an ISO metric thread. However, to accurately determine the thread type, it is necessary to know the thread pitch. With this information, you can compare the pitch with the specifications of ISO metric or UNC threads to determine which standard it corresponds to. To clarify, the thread pitch is the distance between threads expressed in millimeters (measured along the length of the stem). For example, a pitch of 1.5 indicates that the distance between one thread and the next is 1.5 mm.
What if there are still doubts?
In the event that the pitch is not known and there are still doubts about the thread type, you could measure the number of threads per inch or per millimeter. This information can then be used to better identify the thread according to ISO or UNC standards. The thread pitch can also be calculated by measuring the entire length of the thread on a screw and then counting the total number of threads. The length of the thread is then divided by the total number of threads to calculate the pitch.
Are there alternatives?
Alternatively, you can consult technical specifications or use a thread gauge to confirm the exact thread type.
ISO METRIC THREAD
A classic screw identified by an M with a nominal or fine pitch, whose ideal profile is an equilateral triangle; the crests of the threads are chamfered and the bottom of the screw rounded, creating clearance that makes the manufacturing and assembly of the parts easier.
UNC SERIES THREAD
The inch-based UNC thread is the “Unified National Coarse” thread used in the United States. It is comparable to the standard metric thread in Europe.
Visit our website and discover how easy it is for companies to buy our stainless steel fasteners online.
Want to read more articles? Continue here.