KEVOS® MAKEOS · Threads

Unified Inch Thread Gauge Sizes (GO and NOT GO Plugs, Rings and Setting Gauges)

For a Unified inch screw thread with known product limits, what are the nominal sizes and tolerance directions of the GO and NOT GO thread gauges, the plain major and minor diameter gauges, and the setting plugs and rings, and do the gauge tolerances leave room inside the product tolerance?

Nominal sizes and limits of the American National Standard gauges for Unified inch screw threads by the formulas of ANSI/ASME B1.2 Table 5 that the handbook gives: GO and NOT GO (LO) thread ring gauges and plain major diameter gauges for external threads, GO and NOT GO (HI) thread plug gauges and plain minor diameter gauges for internal threads, full-form and truncated setting plugs with the 0.001 in crest-width rule, and solid thread-setting rings for snap and indicating gauges. The product limits and the gauge tolerances (from Table 4 for W and X gauges, and your plain gauge standard) are entered, and each gauge is listed with the side its tolerance is applied to, in inches and millimetres.

Open the calculatorRuns in your browser. No account needed.

How this tool works

Inputs, units and where to find them

InputUnitTypical source
Thread
Threads per inchTPIThreads per inch of the Unified thread; the pitch is p = 1 ÷ n.
External thread (bolt) limits
Maximum major diameterinMaximum major diameter of the external thread, from the thread limits table for the size and class.
Minimum major diameterinMinimum major diameter of the external thread.
Maximum pitch diameterinMaximum pitch diameter of the external thread.
Minimum pitch diameterinMinimum pitch diameter of the external thread.
Internal thread (nut) limits
Minimum major diameterinMinimum major diameter of the internal thread (equal to the basic major diameter).
Minimum pitch diameterinMinimum pitch diameter of the internal thread.
Maximum pitch diameterinMaximum pitch diameter of the internal thread.
Minimum minor diameterinMinimum minor diameter of the internal thread.
Maximum minor diameterinMaximum minor diameter of the internal thread.
Gauge tolerances
Pitch diameter tolerance of the GO and NOT GO thread gaugesinPitch diameter tolerance of the working thread gauges, from Table 4 for the gauge class (X gauges are normal for working gauges) and the thread size.
Major and minor diameter tolerance of the thread gaugesinTolerance on the major and minor diameters of the thread gauges, from Table 4.
W tolerance on pitch diameter (setting plugs and rings)inW gauge tolerance on pitch diameter from Table 4, used for setting plugs and rings.
W tolerance on major and minor diameters (setting gauges)inW gauge tolerance on major and minor diameters from Table 4.
Tolerance of the plain diameter gaugesinTolerance of the plain plug, ring or snap gauges for the major and minor diameters, from the gauge-maker’s tolerance class you specify.

What each input means

Open an input to see what it is, its units, the worked example and the common mistakes, with a small diagram.

Thread

What this means: Threads per inch
Illustration: Threads per inchA screw-thread profile with crests and roots, the pitch from crest to crest and the major and minor diameters, for Threads per inch.pitchmajorminornExample: 20 TPIThreads per inch
What it is
Threads per inch of the Unified screw thread being gauged.
Units and format
Enter a number in TPI: threads per inch. The form accepts 1 TPI to 120 TPI. Required: the tool does not calculate until every input is valid.
Example
The form opens with 20 TPI as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
Effect on the result
Sets the pitch, the sharp-V height H and the setting plug truncation.
Get it right
Read it from the thread designation, for example 20 in 1/4-20 UNC-2A.

External thread (bolt) limits

What this means: Maximum major diameter
Illustration: Maximum major diameterA circle with a line straight through its centre from edge to edge, marking the diameter Maximum major diameter.D_maxmeasured acrossthe centreExample: 0.2489 inMaximum major diameter
What it is
Maximum major diameter of the external thread for its size and class.
Units and format
Enter a number in in: inches. The form accepts 0.000001 in to 40 in. Required: the tool does not calculate until every input is valid.
Example
The form opens with 0.2489 in as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
Effect on the result
Sets the plain GO major gauge and the setting plug majors.
Get it right
Take it from the Unified thread limits table; for class 2A it is the basic major diameter less the allowance.
What this means: Minimum major diameter
Illustration: Minimum major diameterA circle with a line straight through its centre from edge to edge, marking the diameter Minimum major diameter.D_minmeasured acrossthe centreExample: 0.2408 inMinimum major diameter
What it is
Minimum major diameter of the external thread for its size and class.
Units and format
Enter a number in in: inches. The form accepts 0.000001 in to 40 in. Required: the tool does not calculate until every input is valid.
Example
The form opens with 0.2408 in as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
Effect on the result
Sets the plain NOT GO major gauge.
Get it right
Take it from the Unified thread limits table.
What this means: Maximum pitch diameter
Illustration: Maximum pitch diameterA circle with a line straight through its centre from edge to edge, marking the diameter Maximum pitch diameter.E_maxmeasured acrossthe centreExample: 0.2164 inMaximum pitch diameter
What it is
Maximum pitch diameter of the external thread for its size and class.
Units and format
Enter a number in in: inches. The form accepts 0.000001 in to 40 in. Required: the tool does not calculate until every input is valid.
Example
The form opens with 0.2164 in as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
Effect on the result
Sets the GO thread ring and the GO setting plug pitch diameters and the GO ring minor diameter.
Get it right
Take it from the Unified thread limits table.
What this means: Minimum pitch diameter
Illustration: Minimum pitch diameterA circle with a line straight through its centre from edge to edge, marking the diameter Minimum pitch diameter.E_minmeasured acrossthe centreExample: 0.2127 inMinimum pitch diameter
What it is
Minimum pitch diameter of the external thread for its size and class.
Units and format
Enter a number in in: inches. The form accepts 0.000001 in to 40 in. Required: the tool does not calculate until every input is valid.
Example
The form opens with 0.2127 in as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
Effect on the result
Sets the NOT GO (LO) thread ring and setting plug pitch diameters.
Get it right
Take it from the Unified thread limits table.

Internal thread (nut) limits

What this means: Minimum major diameter
Illustration: Minimum major diameterA circle with a line straight through its centre from edge to edge, marking the diameter Minimum major diameter.D_nminmeasured acrossthe centreExample: 0.25 inMinimum major diameter
What it is
Minimum major diameter of the internal thread, normally the basic major diameter.
Units and format
Enter a number in in: inches. The form accepts 0.000001 in to 40 in. Required: the tool does not calculate until every input is valid.
Example
The form opens with 0.25 in as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
Effect on the result
Sets the GO thread plug major diameter.
Get it right
Take it from the Unified thread limits table for the internal class.
What this means: Minimum pitch diameter
Illustration: Minimum pitch diameterA circle with a line straight through its centre from edge to edge, marking the diameter Minimum pitch diameter.E_nminmeasured acrossthe centreExample: 0.2175 inMinimum pitch diameter
What it is
Minimum pitch diameter of the internal thread for its size and class.
Units and format
Enter a number in in: inches. The form accepts 0.000001 in to 40 in. Required: the tool does not calculate until every input is valid.
Example
The form opens with 0.2175 in as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
Effect on the result
Sets the GO thread plug and GO setting ring pitch diameters.
Get it right
Take it from the Unified thread limits table; it equals the basic pitch diameter.
What this means: Maximum pitch diameter
Illustration: Maximum pitch diameterA circle with a line straight through its centre from edge to edge, marking the diameter Maximum pitch diameter.E_nmaxmeasured acrossthe centreExample: 0.2224 inMaximum pitch diameter
What it is
Maximum pitch diameter of the internal thread for its size and class.
Units and format
Enter a number in in: inches. The form accepts 0.000001 in to 40 in. Required: the tool does not calculate until every input is valid.
Example
The form opens with 0.2224 in as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
Effect on the result
Sets the NOT GO (HI) plug pitch and major diameters and the NOT GO setting ring.
Get it right
Take it from the Unified thread limits table.
What this means: Minimum minor diameter
Illustration: Minimum minor diameterA circle with a line straight through its centre from edge to edge, marking the diameter Minimum minor diameter.D1_minmeasured acrossthe centreExample: 0.196 inMinimum minor diameter
What it is
Minimum minor diameter of the internal thread for its size and class.
Units and format
Enter a number in in: inches. The form accepts 0.000001 in to 40 in. Required: the tool does not calculate until every input is valid.
Example
The form opens with 0.196 in as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
Effect on the result
Sets the plain GO minor plug and the GO setting ring minor diameter.
Get it right
Take it from the Unified thread limits table.
What this means: Maximum minor diameter
Illustration: Maximum minor diameterA circle with a line straight through its centre from edge to edge, marking the diameter Maximum minor diameter.D1_maxmeasured acrossthe centreExample: 0.207 inMaximum minor diameter
What it is
Maximum minor diameter of the internal thread for its size and class.
Units and format
Enter a number in in: inches. The form accepts 0.000001 in to 40 in. Required: the tool does not calculate until every input is valid.
Example
The form opens with 0.207 in as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
Effect on the result
Sets the plain NOT GO minor plug and the NOT GO setting ring minor diameter.
Get it right
Take it from the Unified thread limits table.

Gauge tolerances

What this means: Pitch diameter tolerance of the GO and NOT GO t…
Illustration: Pitch diameter tolerance of the GO and NOT GO thread gaugesA nominal size line with an upper and a lower limit around it; parts inside the band are acceptable. The figure illustrates Pitch diameter tolerance of the GO and NOT GO thread gauges.upperlowerT_PDExample: 0.0003 inPitch diameter tolerance of the GO and NOT GO…
What it is
Pitch diameter tolerance of the working GO and NOT GO thread gauges.
Units and format
Enter a number in in: inches. The form accepts 0.000001 in to 0.1 in. Required: the tool does not calculate until every input is valid.
Example
The form opens with 0.0003 in as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
Effect on the result
Widens each thread gauge zone into the product tolerance.
Get it right
Take it from Table 4 for the threads per inch and the diameter; X gauges are usual for working gauges, W gauges for closer work.
What this means: Major and minor diameter tolerance of the threa…
Illustration: Major and minor diameter tolerance of the thread gaugesA nominal size line with an upper and a lower limit around it; parts inside the band are acceptable. The figure illustrates Major and minor diameter tolerance of the thread gauges.upperlowerT_dExample: 0.0005 inMajor and minor diameter tolerance of the thr…
What it is
Tolerance on the major and minor diameters of the thread gauges.
Units and format
Enter a number in in: inches. The form accepts 0.000001 in to 0.1 in. Required: the tool does not calculate until every input is valid.
Example
The form opens with 0.0005 in as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
Effect on the result
Widens the minor diameter zones of rings and the major diameter zones of plugs.
Get it right
Take it from Table 4 for the threads per inch and the diameter.
What this means: W tolerance on pitch diameter (setting plugs an…
Illustration: W tolerance on pitch diameter (setting plugs and rings)A nominal size line with an upper and a lower limit around it; parts inside the band are acceptable. The figure illustrates W tolerance on pitch diameter (setting plugs and rings).upperlowerW_PDExample: 0.0001 inW tolerance on pitch diameter (setting plugs…
What it is
W gauge tolerance on pitch diameter, used for the setting plugs and rings.
Units and format
Enter a number in in: inches. The form accepts 0.000001 in to 0.1 in. Required: the tool does not calculate until every input is valid.
Example
The form opens with 0.0001 in as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
Effect on the result
Widens the setting gauge pitch diameter zones.
Get it right
Take it from the W gauge rows of Table 4.
What this means: W tolerance on major and minor diameters (setti…
Illustration: W tolerance on major and minor diameters (setting gauges)A nominal size line with an upper and a lower limit around it; parts inside the band are acceptable. The figure illustrates W tolerance on major and minor diameters (setting gauges).upperlowerW_dExample: 0.0005 inW tolerance on major and minor diameters (set…
What it is
W gauge tolerance on the major and minor diameters of the setting gauges.
Units and format
Enter a number in in: inches. The form accepts 0.000001 in to 0.1 in. Required: the tool does not calculate until every input is valid.
Example
The form opens with 0.0005 in as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
Effect on the result
Widens the setting plug major and setting ring minor diameter zones.
Get it right
Take it from the W gauge rows of Table 4.
What this means: Tolerance of the plain diameter gauges
Illustration: Tolerance of the plain diameter gaugesA nominal size line with an upper and a lower limit around it; parts inside the band are acceptable. The figure illustrates Tolerance of the plain diameter gauges.upperlowerT_plExample: 0.0001 inTolerance of the plain diameter gauges
What it is
Tolerance of the plain plug, ring or snap gauges for the major and minor diameters.
Units and format
Enter a number in in: inches. The form accepts 0.000001 in to 0.1 in. Required: the tool does not calculate until every input is valid.
Example
The form opens with 0.0001 in as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
Effect on the result
Widens the plain gauge zones inside the major and minor diameter tolerances.
Get it right
Use the gauge-maker’s tolerance class you specify for plain gauges of that size.

Method and formulas

  1. p = 1 ÷ n; H = 0.866025 p, the height of the sharp V.
  2. Thread gauges for external threads: GO PD = max PD (minus); GO minor = max PD − H ÷ 2 (minus); NOT GO PD = min PD (plus); NOT GO minor = min PD − H ÷ 4 (plus). Plain major: GO = max major (minus), NOT GO = min major (plus).
  3. Thread gauges for internal threads: GO major = min major (plus); GO PD = min PD (plus); NOT GO major = max PD + H ÷ 2 (minus); NOT GO PD = max PD (minus). Plain minor: GO = min minor (plus), NOT GO = max minor (minus).
  4. Setting plugs: GO major, truncated = max major − (0.060 ∛p² + 0.017 p) (minus); GO major, full = max major (plus); GO PD = max PD (minus); NOT GO major, truncated = min PD + H ÷ 2 (minus); NOT GO PD = min PD (plus).
  5. NOT GO setting plug major, full portion = max major (W plus), unless the crest would then be narrower than 0.001 in: then max major + 0.216506 p − (PD tolerance + 0.0017) (W minus).
  6. Setting rings: GO PD = min PD of the internal thread (plus); GO minor = min minor (minus); NOT GO PD = max PD (minus); NOT GO minor = max minor (minus).
  7. Example: for 1/4-20 UNC-2A/2B the GO thread ring has a minor diameter of 0.19475 in, the NOT GO (HI) plug a major diameter of 0.24405 in and the truncated GO setting plug 0.23991 in.

Limitations

  • The formulas are ANSI/ASME B1.2-1983 Table 5 as the handbook gives them; lead and half-angle tolerances of the gauges (Table 4) are not calculated here.
  • Enter the product limits from the Unified thread tables for the size, series and class, and the gauge tolerances from Table 4 for the threads per inch and diameter.
  • The truncated setting plug portion is needed only when the optional sharp root profile is used.
  • Tolerances greater than W on the setting ring pitch diameter are acceptable when the indicating or snap gauge can take them and supplier and user agree.
  • Example values are illustrations. Replace them with values for your actual task.

Typical uses

  • Specify the thread gauges to order for a Unified thread
  • Check a gauge maker’s quoted sizes against the standard formulas
  • See how much of the product tolerance the gauge tolerances use

Who it is for

  • Quality inspectors
  • Gauge makers
  • Manufacturing engineers

What you get

  • Sharp-V height H and the setting plug truncation
  • GO and NOT GO thread ring sizes for the external thread
  • GO and NOT GO thread plug sizes for the internal thread
  • Plain major and minor diameter gauge sizes
  • Setting plug and setting ring sizes, with the 0.001 in crest-width rule
  • Each gauge with its tolerance direction and limits in inches and millimetres

Interpreting the result

  • Every gauge tolerance points into the product tolerance: GO gauges are made smaller (rings) or larger (plugs) only towards the NOT GO side, so a part a gauge accepts is always within its limits.
  • When the gauge tolerances take a large share of the product pitch diameter tolerance, good parts near the limits will be rejected; finer gauges or indicating gauges leave more of the tolerance for manufacture.

References

  • Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 2013–2014, 1808. Topic reference; no source tables or recommended settings are reproduced.

Learn the Concepts Behind This Tool

These KEVOS® Library readings explain the method this tool uses, with worked examples.

KEVOS® tools are screening and decision-support utilities. Verify important financial, engineering, safety, legal or operational decisions using appropriate professional standards and your organisation’s approved data.

Open the Unified Inch Thread Gauge Sizes (GO and NOT GO Plugs, Rings and Setting Gauges) calculator

Threads

ISO Metric Thread Basic Dimensions

What are the basic pitch, minor and root diameters and stress area of this metric thread?

About this tool →Threads

Unified Inch Thread Basic Dimensions

What are the basic pitch and minor diameters and stress area of this UNC or UNF thread?

About this tool →Threads

Three-Wire Thread Measurement

What should the measurement over three wires read for this thread, or what pitch diameter does a reading give?

About this tool →Threads

Thread Helix Angle and Screw Efficiency

What is the helix angle of this thread, how efficient is it, and will it self-lock?

About this tool →Threads

Simple Indexing on a Dividing Head

How many crank turns and holes give this number of divisions on a dividing head?

About this tool →Threads

Change Gears for Thread Cutting

Which change gears cut this thread lead on this lathe?

About this tool →