The use of screw gauges is determined by JIS standards.

Use the accuracy class of the drawing instruction and inspect the screws according to the prescribed method.

[Limit gauge for screws types and how to use them]

Name Shape	Plug gauge		Ring gauge
Purpose	For internal thread		For external thread
	GO	NO GO	GO	NO GO
Current JIS 6H, 6g, etc.	GP	NP	GR	NR
Former JIS Class 1~3	GP	WP (Machining)	GR	WR (Machining)
		IP (for inspection)		IR (for inspection)
Use JIS B0251	When screwed in by hand without applying excessive force GO side → You have to go through the whole length NO GO side (current JIS) → Passes if it is not screwed in more than 2 revolutions NO GO side (former JIS) → Pass if you do not enter more than 2 rotations

In the former JIS and the current JIS (ISO), not only the accuracy of the screw has changed, but also the symbol of the gauge has also changed.
The GO side of a plug gauge has always been GP, ​​but the NO-GO side is NP in the current JIS standard, while the previous JIS standard was divided into two types: WP for machining and IP for inspection.
Former JIS NO GO sides are divided into two types: WP for machining and IP for inspection.
The same is true for ring gauges, where GO is GR.
On the NO GO side, there are NR of the current JIS and WR/IR of the former JIS.

* How to use the gauge
There is a slight difference between the current JIS and the former JIS in terms of the passing conditions on the NO GO side.
When screwed by hand without excessive force,
GO must go through overall length .

・ISO (current JIS)
The current JIS NO GO side, which determines the pass/fail of 6H ( internal thread accuracy) and 6g ( external thread accuracy) thread accuracy, is
If it is not screwed in more than 2 turns, it will pass

・Former JIS
The former JIS NO GO side, which determines the pass/fail of the thread accuracy of class 1 and class 2, passes if it does not enter more than 2 rotations.

If you read exactly, when it was just 2 turns,
It passes the current JIS and fails the former JIS.
However, depending on the feelings of the user, it is just two revolutions that will be doubtful
I think that it is a source of trouble to consider it as a pass.
A good screw that is properly made to the hole entrance and tip often does not fit a single turn.
For screws that hold a NO GO gauge for nearly two turns, it is a good idea to check the machining status, including the tool.

・Limit gauge
The limit method used in the term limit screw gauge is:
It is to check the minimum and maximum to prove that it is within the specified tolerances.
The thread limit gauge verifies that the pitch diameter of the screw is within the tolerance.
In addition, there is also a gauge called a plug gauge that does not have a screw.
This inspects whether the hole diameter is within the tolerance.