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Ring Gage Basics
Guide · Updated October 28, 2026
A ring gage is a hardened, lapped ring used to check an outside diameter. A plain go ring sits at the largest allowed shaft size and must slide on; the no-go ring sits at the smallest size and must not.
Check the ring too
Spot-check micrometers used alongside ring gages with an exact stack from the free Gage Block Calculator.
Step by step
- Find the shaft limits: Read the maximum and minimum diameter from the drawing, for example 0.7500/0.7495 in.
- Select the rings: GO ring = maximum shaft size; NO-GO ring = minimum shaft size, usually marked with a groove on the OD.
- Clean and cool: Wipe the ring and the part, and let a freshly cut part cool to room temperature.
- Check GO: Slide the GO ring over the full length of the diameter with no force. It must pass.
- Check NO-GO: Present the NO-GO ring square to the shaft. It must not start beyond a slight lead-in.
- Accept and store: Accept only if GO passes and NO-GO does not; wipe, oil and store the rings.
Worked example
A shaft is toleranced 0.7500 +0.0000/−0.0005 in. GO ring = 0.7500 in, NO-GO ring = 0.7495 in.
Because the GO ring checks the whole length at once, it also catches taper, bends and lobing that a micrometer reading at one spot can miss. A shaft measuring 0.7498 in on a mic but bowed by 0.0004 in can still fail the GO ring, and that is the correct result for a mating bore.
Setting rings vs go/no-go rings
Setting (master) rings are single sizes used to zero bore gages and internal micrometers, not to accept parts. Thread ring gages work the same go/no-go way for external threads; see thread gage basics.
Tips
- Never tap a ring on with a mallet; if it binds, the part is oversize or dirty.
- Pair with the hole side: plug gage basics.
- For the full go/no-go concept: go/no-go gaging basics.
- Pin gages handle the hole side of quick checks: pin gage set basics.
- Snap gages are faster for production ODs: how to set a snap gage.
FAQ
What is a go/no-go ring gage?
A pair of rings for checking a shaft: the GO ring is the maximum size and must pass over the part; the NO-GO ring is the minimum and must not.
How do you tell the NO-GO ring?
It is usually marked NO-GO or NOT GO and often has a groove or red band on its outside diameter.
Ring gage or micrometer?
A micrometer gives a number at one spot; a GO ring checks the full length and form, which matters for a mating fit.
What is a setting ring?
A master ring of known size used to zero bore gages and internal measuring tools.
Is there a free gage block calculator?
Yes. The Gage Block Calculator at gageblockcalc.com builds any stack, free with no login.
Related guides and calculators
- Plug gage basics
- Go/No-Go gaging basics
- Pin gage set basics
- How to set a snap gage
- Thread gage basics
- ISO 286 fit calculator
- How to Hone a Bore
- How to Check Plug Gage Wear
- How to Set a Bore Gage
- How to Use a Dial Snap Gage
- How to Use a CNC Touch Probe
- All free machinist calculators
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General shop information only — follow your tooling, machine and gage manufacturers' instructions and your quality system.