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Thread Limit Gauges / ISO standards

Thread limit gages are rated according to the tolerance class of threads to be measured with them. Threads are judged acceptable if the go-gage smoothly and completely enters them but the no-go gage does not enter more than two turns. In addition to these JIS thread limit gages, we design and manufacture various types of thread gages based on every standard.

Thread Limit Gauges / ISO standards

Construction of model

Thread Limit Gauges / JIS standards

Thread Limit Gauges / JIS standards

Differences between the ISO gauges standard and the conventional JIS gauges standard (or features of the ISO gauges standard)
Check gages and production gauges are not distinguished any more on both the go end and no-go end of gauges.
The ISO gauges standard makes no distinction between the no-go end of check gauges and that of production gauges, though they were distinguished in the conventional JIS. Therefore, threads can be judged acceptable if they are proved to satisfy the standard through a check using either check or production gauge which is known to meet the requirements (with possible wear being taken into consideration).
As gages for external threads, ring gauges have been added to the snap gauges in order to satisfy the Tayler's principle.

Pass/fail judgement of thread ring gauges
The conventional JIS gauges standard provided that ring gauges might be judged acceptable if the fit check gauges smoothly entered them without producing play. In the ISO gauges standard, however, thread ring gauges are to be checked with two fit check gages: a go gauges and a no-go gauges, and they are judged acceptable if the go gauges enters them smoothly and completely but no-go gauges does not enter more than one turn.

Thread plug gauges for checking wear
The no-go end of thread plug gauges for checking wear was not standardized by JIS, and therefore it was necessary for users to set their own standard for the no-go end of their gauges, considering both the increase in the useful life of the gauges and the decrease in the acceptance rate of the threaded products. Recently, however, the ISO gauges standard has been introduced into JIS.

Metric coarse pitch thread

Tolerance quality Male / female Applicable range ISO grade JIS grade
Precise class Female thread M1 or more 4H(M1.4 or less) Class 1
Male thread M1 or more 5H(M1.6 or more) Class 1
Female thread M1 or more 4H Class 1
Precise Female thread M1 or more 5H(M1.4 or less) Class 2
Female thread M1 or more 6H(M1.6 or more) Class 2
Male thread M1 or more 6H(M1.4 or less) Class 2
Male thread M1 or more 6G(M1.6 or more) Class 2
Coarse Female thread M3 or more 7H Class 3
Male thread M5 or more 8G Class 3

Metric fine pitch thread

Tolerance quality Male / female Applicable range ISO grade JIS grade
Precise class Female thread M1x0.2 or more 4H(M1.8x0.2 or less) Class 1
Female thread M1x0.2 or more 5H(M2x0.25 or more) Class 1
Male thread M1x0.2 or more 4H Class 1
Precise Female thread M2.5x3.5 or more 6H Class 2
Male thread M1x0.2 or more 6H(M1.4x0.2 or less) Class 2
Male thread M1x0.2 or more 6G(M1.6x0.2 or more) Class 2
Coarse Female thread M4x0.5 or more 7H Class 3
Male thread M8x1.0 or more 8G Class 3

Construction of model

Thread Limit Gauges / Parallel Pipe Thread Gauges

Used to check parallel pipe threads. In the current JIS which has introduced the ISO gauges standard, parallel pipe threads are referred to as 'G', instead of 'PF', as far as the ISO standard is concerned.

Thread Limit Gauges / Parallel Pipe Thread Gauges

JISMethodSymbolTypeClassRange
JISISO StandardGStraight pipe male threadClass A, B1/16-6
JISISO StandardGStraight pipe female thread-1/16-6
JISFormer JIS appendixPFStraight pipe Male threadClass A, B7-12
JISFormer JIS appendixPFStraight pipe female threadClass A7-12
-Former JIS appendixPFStraight pipe Male threadClass A, B1/8-6
-Former JIS appendixPFStraight pipe female threadClass A1/8-6

Thread Limit Gauges / Standard Thread Gauges

Every standard thread gage, composed of a pair of gages precisely fitted together, has nearly the same size as the basic size of applicable threads. To check a product thread with this gage, you need to fit it directly onto the thread in most cases.

Thread Limit Gauges / Standard Thread Gauges

Tapered Thread Gauges / Taper Pipe Thread Gauges R

Used to check taper pipe external and internal threads, and parallel pipe internal threads to be engaged with taper external threads. In the current JIS which has introduced the ISO gage standard, taper pipe threads are referred to as 'R' or 'RC', instead of 'PT', as far as the ISO standard is concerned.

Tapered Thread Gauges / Taper Pipe Thread Gauges R

Example
Taper thread plug gaugeR11/2
Taper thread ring gaugeR11/2
Plug gauge for inspection 

*No symbol for taper thread plug gauge & ring gauge

Tapered Thread Gauges / Taper Pipe Thread Gauges PT

In a check using this type of gage, pipe threads are judged acceptable if the end of the pipe or pipe joint (excluding the chamfer of parallel pipe internal threads) falls within the notched area when the gage is fitted and tightened by hand.

Tapered Thread Gauges / Taper Pipe Thread Gauges PT

Inspection thread product

 Symboltype
Standard threadRTaper pipe Male thread
Standard threadRcTaper pipe Female thread
Standard threadRpTaper pipe Female thread
Appendix threadPTTaper pipe Male thread
Appendix threadPTTaper pipe Female thread
Appendix threadPSStraight pipe Female thread

Inspection of thread product

Symboltype
RTaper thread ring gauge
RTTaper thread ring gauge

Tapered Thread Gauges / Taper Pipe Thread Gauges (US Standard)

Typical standards widely used at present
Ordinary threads : NPT (American (National) Standard Taper Pipe Thread) Sealing threads : NPTF (Dry seal American Standard Taper Pipe Thread) Aeronautical threads : ANPT (Aeronautical National Standard Taper Pipe Thread)

Tapered Thread Gauges / Taper Pipe Thread Gauges (US Standard)

Plain Gauges / Morse Taper Gauges / National Taper Gauges

Taper gages are used to check the tapers and reference diameters (diameters of the large and small end faces) of tapered products. This type of gage consists of a set of gages fitted together: a taper plug gage and a taper ring gage.
Main types of taper are Morse taper, national taper and Brown & Sharp taper. Products can be judged by the point up to which their reference end face goes into the gage with a notch, or by the line drawn on the larger end face of the taper plug gage.

Plain Gauges / Morse Taper Gauges / National Taper Gauges

Plain Gauges / Limit Gauges

Every limit gage has two measuring end faces: one for the allowable maximum size of the hole or shaft and the other for the allowable minimum size. Since the tolerances of limit gages are set in connection with the tolerances of applicable product holes or shafts, and thus the levels of difficulty in manufacturing them vary depending on the tolerance, the tolerance ratings are set according to the rating of applicable holes or shafts and the type of limit gage.

Plain Gauges / Limit Gauges

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