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 |