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Pin Gage Set Basics
Guide · Updated October 27, 2026
Pin gages (plug gage pins) are the fastest way to size a small hole or set a go/no-go check. A set of pins in 0.001 in steps covers almost every drilled and reamed hole in a shop. Here's how to choose class and sign and how to keep them accurate.
Verify your pins
Set your comparator or check your micrometer with a stack from the free Gage Block Calculator. Free, no login.
Classes (inch, commonly cited)
| Class | Tolerance | Typical use |
|---|---|---|
| ZZ | ±0.0002 in | Shop sets, hole sizing |
| Z | ±0.0001 in | Tighter go/no-go |
| Y, X, XX | ±0.00007 to ±0.00002 in | Gauge and lab work |
Check your supplier's spec. Tolerances can grow with pin diameter.
Step by step
- Pick the class: ZZ for general shop work, tighter classes for gauge work.
- Pick plus or minus: Plus for go gauges, minus for no-go.
- Check the pins: Mic a sample of pins against a micrometer checked with gage blocks.
- Use without force: A pin should enter under its own weight or with a light push. Never force it.
- Store and track: Keep pins in their numbered holes and replace any that are worn or rusted.
Related checks
- Go/no-go sizing and the 10% rule: go/no-go gaging basics.
- Pins as radius references: checking radius gages.
- Larger holes: bore gages.
FAQ
What are pin gage classes?
Classes set the size tolerance of each pin. From loosest to tightest they're commonly ZZ (±0.0002 in), Z (±0.0001), Y (±0.00007), X (±0.00004) and XX (±0.00002). Class ZZ is standard for shop pin sets.
Should I buy plus or minus pins?
Plus pins are oversize within their tolerance, so they suit go gauges for holes. Minus pins are undersize and suit no-go gauges. Both keep the gauge tolerance inside the part tolerance.
What sizes come in a pin gage set?
Inch sets usually step by 0.001 in over a range, for example 0.061–0.250 or 0.251–0.500 in. Metric sets step by 0.01 mm.
How do I check pin gages?
Mic them with a micrometer checked against gage blocks, or compare them on a bench comparator set with a stack. Build the stack free at gageblockcalc.com.
Can I use pins to measure a hole?
Yes. The largest pin that enters freely gives the hole size to about 0.001 in. It doesn't show roundness or taper.
Related guides and calculators
- Metric dowel pin chart (ISO 8734)
- Taper pin chart (ASME B18.8.2)
- Slotted spring pin chart (ISO 8752)
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- How to wring gage blocks
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- Gage block care and wear blocks
- Feeler Gage Basics
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- How to Set a Snap Gage
- How to Use Small Hole Gages
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- Coiled spring pin chart (ISO 8748)
- Inch roll pin chart (ASME B18.8.2)
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Build your stack in seconds
The free Gage Block Calculator finds the fewest-block combination for inch and metric sets, with wear blocks. No login.
Questions? Ask a machinist.
General shop information only — follow your gage manufacturer's instructions and your quality system.