Plug gauge calibration: how often, to which standards, and how
A plug gauge is a fixed-limit gauge used to verify that internal diameters such as drilled or reamed holes fall within tolerance, typically as a go/no-go pair. Because the gauge itself is the acceptance criterion, wear on the go member directly causes false accepts, so periodic dimensional calibration against traceable standards is essential.
Also known as: plug gage, plain plug gauge, go/no-go plug gauge, cylindrical plug gauge, pin gauge
How often should a plug gauge be calibrated?
High-use gauges warrant quarterly or even monthly verification; recalibrate immediately after drops, overload, or visible damage, and test new hardened gauges after the first year to evaluate hardened steel growth.
Where this number comes from
No standard mandates a recalibration interval for hardened fixed-limit gauges; gauge makers state that frequency must be set per gauge from usage and wear history. Calibration providers such as Techmaster commonly recommend every 6 to 12 months as a starting point, with quarterly or even monthly checks for high-use environments.
Calibration intervals are a risk-based decision for the instrument owner, not a fixed rule: guidance documents such as ILAC-G24 and OIML D 10 describe how to set and adjust them from usage, criticality and calibration history. Treat the interval above as a starting point for your own quality system, not a compliance requirement.
What shortens or lengthens the interval
- Number of parts gauged per day, since every insertion of the go member abrades its surface
- Hardness and abrasiveness of the workpiece material (soft plastic wears the gauge far more slowly than hardened steel or abrasive castings)
- Criticality of the toleranced holes, because a worn undersized go member produces false-pass results
- As-found drift and wear trend documented on previous calibration certificates
- Cleanliness of the gauging environment, since grit and chips accelerate wear
- Handling risk such as drops and corrosion from skin contact without preservation oil
Standards relevant to plug gauge calibration
Defines plain limit gauge types including full form cylindrical plug gauges, their design and metrological characteristics, and the new and wear limit maximum permissible limits (MPLs) used as calibration acceptance criteria; second edition published 2026 replacing ISO 1938-1:2015.
Establishes uniform practices and tolerances for measuring plain external diameters of cylindrical plug gauges; 1998 edition reaffirmed 2024.
Standards are referenced by designation and title. For normative requirements, always work from the current edition of the standard itself.
How a plug gauge is calibrated
A typical plug gauge calibration, in an accredited lab or in-house, follows this outline. The exact points, tolerances and paperwork come from the applicable standard and your own procedure.
- Visually inspect the gauge for nicks, scratches, corrosion, and contamination; clean and demagnetize before measurement
- Thermally stabilize the gauge and reference standards in the lab environment (nominally 20 degrees C) before measurement
- Record as-found diameter measurements on both go and no-go members using a universal length measuring machine or comparator set with gauge blocks or master discs
- Measure at multiple axial positions and orientations to detect taper, out-of-roundness, and localized wear at the entry threads of the gauging surface
- Compare as-found values to the gaugemaker class tolerance and the wear limit MPLs defined in ISO 1938-1 for the gauge class
- Disposition the gauge: pass, downgrade, or remove from service (plain plug gauges are not adjustable, so worn gauges are retired or reworked)
- Record as-left values and issue a calibration certificate with traceable uncertainty
Reference equipment typically used
- Universal length measuring machine or bench micrometer/supermicrometer
- Grade 0 or K gauge block set
- Master discs or master ring gauges
- Temperature-controlled lab at 20 degrees C
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Sources
- Techmaster Electronics, "Plug Gage Calibration That Stands Up to Audits" (calibration provider guide)
Interval claim: recommends calibration every 6 to 12 months as the most common interval, with quarterly or even monthly checks for high-use environments and recalibration after any damage; also supports the as-found/as-left procedure flow.
- Ring & Plug Thread Gages (Westport Gage), "Calibration Frequency for Hardened Tooling" technical note
Interval basis honesty: states no specified recalibration frequency exists for hard gauges or GO/NOGO gauges, recommends testing after the first year for hardened steel growth, and bases frequency on usage volume, workpiece material, and environment.
- ISO 1938-1:2026, Geometrical product specifications (GPS) - Dimensional measuring equipment - Part 1: Plain limit gauges of linear size, International Organization for Standardization
Standard confirmation: gauge types, design and metrological characteristics, and new/wear limit MPLs used as acceptance criteria.
- ASME B89.1.5-1998 (R2024), Measurement of Plain External Diameters for use as Master Discs or Cylindrical Plug Gages, The American Society of Mechanical Engineers
Standard confirmation: measurement methods and tolerances for plain cylindrical plug gauge diameters.
Cite this data
Gaugelog Calibration Interval Reference, v1.0 (July 2026). 68 instrument types, 236 verified sources. Licensed CC BY 4.0.
Download as CSV or JSON. Intervals are typical starting points, not compliance requirements; every row cites its sources.
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