Gage Maker Tolerances by Size

A gage-maker tolerance describes the permitted variation in the gage itself. It is separate from the workpiece tolerance that the gage checks. The chart below transcribes selected cylindrical gage diameter ranges and tolerance classes from Vermont Gage’s published chart, with inch and metric ranges shown in their own units.

Gage Maker Tolerances by Nominal Size

MECHANITEC / ENGINEERING REFERENCE

Vermont Gage cylindrical gage-maker tolerances

Published diameter ranges and tolerance class values for cylindrical gages in inch and metric units.

1–14 of 14 matching rows (14 total)

Vermont Gage cylindrical gage-maker tolerances — page 1 of 1
Nominal diameter range	Range and tolerance unit	Class XX (in or mm)	Class X (in or mm)	Class Y (in or mm)	Class Z (in or mm)	Class ZZ (in or mm)
0.010–0.825	in	0	0	0	0	0
0.825–1.510	in	0	0	0	0	0
1.510–2.510	in	0	0	0	0	0
2.510–4.510	in	0	0	0	0	0
4.510–6.510	in	0	0	0	0	0.001
6.510–9.010	in	0	0	0	0	0.001
9.010–12.010	in	0	0	0	0	0.001
0.254–20.96	mm	0.001	0.001	0.002	0.003	0.005
20.96–38.35	mm	0.001	0.002	0.002	0.003	0.006
38.35–63.75	mm	0.001	0.002	0.003	0.004	0.008
63.75–114.55	mm	0.001	0.003	0.004	0.005	0.01
114.55–165.35	mm	0.002	0.003	0.005	0.006	0.013
165.35–228.85	mm	0.002	0.004	0.006	0.008	0.016
228.85–305.05	mm	0.003	0.005	0.008	0.01	0.02

Search and sort apply to all 14 rows. Print and CSV include only the 14 rows shown on this page.

Select the correct range and class

First identify the gage’s nominal diameter and find the row whose size interval includes it. Then select the tolerance class required by the inspection plan or drawing. The same nominal size can have different permitted gage variation under classes XX, X, Y, Z and ZZ. Do not treat the columns as workpiece fit classes or as a tolerance for the part being inspected.

Vermont Gage’s chart associates these diameter limits and class values with ASME B89.1.5. The values are the manufacturer’s published gage-tolerance chart; actual gages can have additional customer requirements, construction differences, calibration documentation and special limits. Verify the selected product and class with the gage supplier before ordering.

How gage tolerance affects the inspection decision

A fixed limit gage is a pass/fail tool. A GO plug checks the lower limit of a hole and should enter when the hole is acceptable at that boundary. A NO-GO plug checks the upper limit and should not enter. Ring gages check external dimensions. This approach does not report the actual part size, and the tolerance on the gage affects how close the inspection result is to the workpiece limits.

Vermont Gage explains a common 10% rule for choosing gage tolerance: reserve a portion of the product tolerance for gage variation and allocate it between the GO and NO-GO gages. Its worked example starts with a hole from 0.250 to 0.254 in and demonstrates a suggested Class ZZ value. This is a selection guideline, not a universal requirement. The 10% approach can cause some acceptable parts near the limit to fail inspection, while keeping the gage tolerance inside the part limits helps prevent an out-of-tolerance part from being accepted.

Keep units and direction straight

Use the inch rows for gages specified in inches and the metric rows for gages specified in millimetres. The chart’s metric values are reported to micrometre-level increments; do not convert a rounded inch value and substitute it for a metric class value. Direction matters too: a GO plug commonly carries its tolerance on the plus side and a NO-GO plug on the minus side. Ring-gage directions are reversed in the manufacturer’s guidance.

These directions apply to the relevant gage type and inspection setup. Thread gages, taper gages, setting masters, special-purpose gages and customer-specific gages may follow other rules. Confirm the gage design and governing standard rather than transferring a plain cylindrical plug-gage example to a different gage.

Care, calibration and records

Clean the part and gage before use, remove burrs, and do not force the gage into the part. Keep the gage and workpiece at a stable, similar temperature; dimensional changes can affect a close inspection. Store the gage to protect it from corrosion, impact and wear. Establish calibration frequency from the use rate, workpiece abrasiveness, tolerance and quality procedure, then retain the calibration record and traceability information.

Use this chart to choose a candidate class and discuss the inspection plan. The gage certificate and the current manufacturer information govern the individual instrument. For a critical or disputed measurement, follow the organization’s measurement decision rule and uncertainty process.

Source

Ranges, tolerance classes and the 10% rule notes were checked against Vermont Gage’s Gage Tolerance Selection guide and its 2026 product catalog. The data is specifically a manufacturer’s cylindrical gage tolerance reference; verify the required class against the current drawing, quality plan and gage order.