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Accuracy class of screws
The grade of the screw is generally determined in the drawing at the time of design of the threaded product.
In order to meet the thread accuracy of the drawing instructions, it must pass the inspection with the thread gauge.
The approximate application is shown in the table, but please check the drawing instructions for selecting the gauge for screw machining.
Thread accuracy is expressed by the following grades.
Accuracy (grade) of various screws
| name | Grade of screw | ||||||
| Types of screws | division | Tough ←←←←←← →→→→→→ Loose | |||||
| Metric thread (M) | Conventional JIS | 1st grade | Level 2 | Level 3 | remarks | ||
| Current JIS | external thread | ４ｈ |
6h (M1.4 or less) 6g (M1.6 or higher) |
８ｇ |
alphabet lowercase |
||
| internal thread |
4H (M1.4 or less) 5H (M1.6 or higher) |
5H (M1.4 or less) 6H (M1.6 or higher) |
７Ｈ |
alphabet capital letter |
|||
| Unified Screw (U) |
JIS ANSI |
external thread | ３Ａ | ２Ａ | １Ａ |
Unified Screws If you get a 3, it will be a severe grade. |
|
|
JIS ANSI |
internal thread | ３Ｂ | ２Ｂ | １Ｂ | |||
| Wit Screw (W) | Level 2 | Level 3 | Level 4 | ||||
| Usage | Screws that require a tight fit | For tightening of general machinery | General machine chore screws | Black Skin Bolt |
|
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* About the conventional JIS and the current JIS: The JIS standard for metric threads was revised in 1973.
See below for details. What is the revision of the JIS standard for metric threads?
The allowable dimensions for each grade (tolerance range class) in a typical size of metric thread are as follows.
