ISO thread

The International Organization for Standardization, ISO, tries to limit the number of thread cuts from over 100 to a few that will receive an ISO thread profile.


Stigning – pitch, yderdiameter – outside diameter, delediameter – pitch diameter, inderdiameter – inside diameter, gevindaksel – threaded shaft

Theoretical ISO Thread Profile 

In the following, the ISO Thread Profile is common for screws and nuts:

D2, d2, D1 and d1 can be calculated by using the following formulae:











 


ISO Metric Thread Standard
ISO Inch Thread Standard
ISO Piping Thread Standards

The letter M characterizes the ISO Metric Thread Standard.

Examples:
 

ISO metric coarse thread, nuts

M 10 - 6 H

ISO metric thread standard

M        

Thread dimension

  10      

Tolerance grades for pitch diameter

      6  

Tolerance positioning for pitch diameter

        H

 

 

ISO metric fine-pitch thread, screw

M 10 x 0.75 - 6 h

Thread symbol

M            

Thread dimension

  10          
Pitch       0.75      

Tolerance grades for pitch diameter

          6  

Tolerance positioning for pitch diameter

            h

 

 

ISO metric thread standard

M 10 - 6H / 5g 6g

Thread symbol

M            

Thread dimension

  10          

Tolerance for pitch diameter, nuts

      6H      

Tolerance for pitch diameter, bolts

          5g  

Tolerance for major diameter, blots

            6g


If a thread has no tolerance specification, the 6g for bolts and 6H for nuts are used.

ISO Inch Thread Standard.

UNC   - coarse thread
UNF    - fine-pitch thread
UNEF -  extra fine-pitch thread
UN      - in addition to the above mentioned, these standardized pitches have a finer cut than the UNC
UNS   - the thread has a standardized profile, size and tolerance have been calculated through a table


Examples of ISO Inch Thread Standards:

 

ISO inch thread, coarse

5/16 18 UNC 3A PD 0.2764-0.2792

Thread dimensions in inches

5/16        

Number of thread cuts per inch

  18      

Thread symbol

    UNC    

Tolerance grade

      3A  

PD= pitch diameter with tolerance

        PD 0.2764 - 0.2792

 

If nothing else is stated, the threads are right handed.
Left handed threads are characterized LH (left hand).

Threads under 1/4 inches carries numbers to indicate size.

 

ISO inch thread standard, fine

4 48 UNF

Thread dimension: 0.112 inches = 2.845mm

4    

Threads per inch

  48  

Thread symbol

    UNF