Answer
Check Fixture vs Gauge: Which One Your Part Needs
One feature, one limit: a gauge. A whole part on its datums, several features at once: a fixture.
A gauge checks one feature against one limit: a plug or pin gauge for a hole, a ring for a shaft, a thread gauge for a tapped hole, each made to a gagemaker class. A check fixture holds the whole part on its datums and checks several features at once with pins, blocks or indicators. Order a gauge for a single hole or thread, a fixture for a hole pattern, a profile or a formed part. Both are quoted in 24-48 hours at /quote/.
Updated September 2026
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A gauge checks one feature to a class
A gauge is built to one feature and one limit. A go/no-go plug checks a hole: the GO end must enter, the NO-GO end must not, and the result is pass or fail, not a number. A pin gauge checks a hole at one diameter, a ring gauge checks a shaft, and a thread gauge checks a tapped or external thread under ASME B1.2, asme.org/codes-standards/find-codes-standards/b1-2-gages-gaging-unified-inch-screw-threads, the gauging standard for Unified inch screw threads.
The gauge itself is made to a gagemaker class. Meyer Gage Company’s plug gauge guide, published by Newman Tools at newmantools.com/meyer/pluggage_ABC.htm, lists the classes for 0.0009 to 0.8250 in: XX at 0.000020 in, X at 0.000040 in, Y at 0.000070 in, Z at 0.000100 in and ZZ at 0.000200 in. Measuring a plain plug to its class is the subject of ASME B89.1.5, asme.org/codes-standards/find-codes-standards/measurement-of-plain-external-diameters-for-use-as-master-discs-or-cylindrical-plug-gages. More at /parts/custom-gauges/.
A check fixture locates the whole part and checks several features at once
A check fixture asks whether the part, sitting on its datums, has every checked feature where the print puts it. The locators are the part’s datum features: a flat net for datum A, a pin for datum B, a second pin or a stop for datum C. Once the part is on those three, every other feature is checked relative to them.
The checks come in two kinds. Attribute checks say yes or no: a hardened pin that must pass through a hole, a flush block a formed edge must sit level with, a profile block an edge must fall within. Variable checks return a number from an indicator in a bushing or a height gauge against a datum pad. A CMM holding fixture is a third case: it only locates and holds the part, and the CMM measures. All three are quoted from the print at /parts/fixtures/.
Which one your part needs
One hole or one thread with a tolerance on the print: a gauge. A 0.250 in hole toleranced +0.004/-0.000 in, a 1/4-20 UNC-2B tapped hole or a 0.500 in shaft is a single plug, thread or ring gauge. A hole pattern, a profile, or a formed or molded part with a datum scheme: a fixture, because the question is position relative to datums.
Many parts need both: the fixture checks the pattern and profile, and a thread gauge on a lanyard checks the tapped holes while the part sits in it. For a new part number at program launch, /who-makes-custom-check-fixtures/ covers who to send it to. If budget comes first, /custom-fixture-cost/ lists what drives fixture cost without figures, since every fixture is priced from its own print.
The 10:1 rule applies to both, in different ways
The measuring instrument should resolve to about one-tenth of the tolerance it checks. George Schuetz of Mahr Inc. explains the rule in Modern Machine Shop at mmsonline.com/articles/the-rule-of-thumb-part-1: a 0.0002 in tolerance calls for a gauge reading in 20 microinch increments, the gauge itself is held to about 4 percent of the tolerance so the whole process lands at 10 percent, and a master is chosen at 10 percent of the part tolerance.
For a plug gauge the same idea is the Meyer guide’s 10 percent rule: give 10 percent of the product tolerance to the gauges and the other 90 percent passes whenever the GO fits and the NO-GO does not. Their example: a 0.004 in product tolerance, 0.0004 in to the gauges, a GO plug at 0.250 +0.0002 in and a NO-GO at 0.254 -0.0002 in, class ZZ. For a fixture the rule sets how tightly its own pins and datums are built: checking position within 0.010 in needs pins located near 0.001 in. Callouts are explained at /cnc-machining-tolerances/.
Materials: hardened tool steel for gauges, tooling plate for fixture bases
Gauges are hardened so they keep their size, usually A2 or D2 tool steel. Cincinnati Tool Steel’s A2 data sheet at cintool.com/documents/air_hardening/a2.pdf charts the tempering response: about 62 HRC after a 300 °F temper and 60 HRC after 400 °F. A gauge is ground to size in its hardened condition, the route the hardened punches take, with precision grinding for the diameters, quoted to the class on the print, and wire EDM cutting profile blocks in hardened stock.
Fixture bases are usually cast aluminum tooling plate because it arrives flat and stays flat. Alcoa’s MIC6 brochure, hosted by Yarde Metals at yarde.com/docs/products/mic-6_brochure.pdf, gives plate flatness as 0.005 in (0.127 mm) for 3/4 in thickness and over and 0.015 in (0.381 mm) between 1/4 and 5/8 in, with a 20 microinch surface maximum; ATP-5 is the equivalent 5083-based plate. The pins, nets and bushings that touch the part are hardened A2 or D2, replaceable without remaking the plate.
What to send for each, and how each is inspected
For a gauge, send the feature it checks, the tolerance on the print and the gagemaker class you want; a hole and its limits, or a thread callout such as 3/8-16 UNC-2B, is enough. For a fixture, send the production part’s model and print with its datum scheme, the features to check and how, the quantity and the finish. The full list, hardware BOM and marking included, is at /what-to-send-for-a-custom-fixture/.
Each is inspected against its own print before it ships. Upload any file type at /quote/; STEP plus PDF is ideal. A person quotes in 24-48 hours. Standard lead time is 4-6 weeks. Rush 1-2 weeks applies to machined parts with no secondary operations. Heat treat, grinding, EDM and finishing add time, and the quote gives the real date. Lead time starts at order approval. Put your need date in the part description and the quote answers it.
Questions
Before you send a job.
01 What is the difference between a gauge and a check fixture?
A gauge checks one feature against one limit and returns pass or fail. A check fixture locates the whole part on its print datums and checks several features at once. A single hole or thread wants a gauge; a hole pattern, a profile or a formed part wants a fixture.
02 Is a checking fixture the same thing as a gage?
No. A gage, or gauge, is a single-feature instrument built to a gagemaker class, for example a class Z plug held to 0.000100 in. A checking fixture is a plate with locators that holds the part and carries checks laid out to the print. Both are quoted at /quote/.
03 When is a CMM holding fixture the right choice instead of a check fixture?
When the CMM does the measuring and the fixture only has to hold the part the same way every time. It locates the part on its datums, leaves the checked features clear for the probe and carries no pins, blocks or indicators of its own.
04 How does the 10:1 rule decide the gauge class?
Give 10 percent of the part tolerance to the gauge and pick the class that fits inside it. In the Meyer Gage example a 0.004 in product tolerance leaves 0.0004 in for the gauges, which a class ZZ pair at 0.0002 in each satisfies.
05 How is a gauge or fixture inspected before it ships?
Every gauge and every fixture is inspected against its own print before it ships. Put the gagemaker class or the fixture tolerances on the print, and the quote works from them.
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