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How to Set and Check a Bore Gage with Gage Blocks
Guide · Updated October 27, 2026
A dial bore gage only compares. It reads how far a bore is from the size you set it to, so the setting is everything. With a gage block stack and a pair of accessory jaws you can build a master for almost any bore size and check the gage's reading as well.
Any bore size, fewest blocks
Type the bore size into the free Gage Block Calculator to get the stack. Free, no login.
Setting stacks
| Bore | Stack | Linearity checks |
|---|---|---|
| 1.250 in | 1.000 + 0.250 (81-piece) | 1.252 = 1.000 + 0.150 + 0.102 · 1.248 = 1.000 + 0.148 + 0.100 |
| 2.000 in | 2.000 | 2.002 = 1.000 + 0.900 + 0.102 · 1.998 = 1.000 + 0.850 + 0.148 |
| 32 mm | 30 + 2 (88-piece) | 32.02 = 30 + 1.02 + 1 · 31.98 = 20 + 9.5 + 1.48 + 1 |
Check each total yourself, or let the calculator do it. The method is in how to build a gage block stack.
Step by step
- Build the stack: Build the fewest-block stack equal to the nominal bore size.
- Add jaws: Wring a half-round jaw on each end so the jaws form an inside gap equal to the stack.
- Clamp in a holder: Clamp gently in the accessory holder and let it reach room temperature.
- Zero the bore gage: Insert the gage, rock it to find the turning point, and zero the dial there.
- Check linearity: Set a stack a little larger and smaller, for example ±0.002 in, and confirm the dial reads the difference.
Tips
- Don't over-tighten the holder, because clamping force can shrink the gap.
- Hold the bore gage by its insulated handle. Hand heat grows both the gage and the stack.
- Jaws, holders and bases are covered in gage block accessories.
- Checking other gauges? See micrometers, calipers and dial indicators.
FAQ
Can you set a dial bore gage with gage blocks?
Yes. Wring a stack equal to the bore size, add a pair of half-round jaws from an accessory set, and clamp it in a holder. The gap between the jaws equals the stack length, so you can zero the bore gage in it like a ring gage.
What stack sets a 1.250 inch bore gage?
1.000 + 0.250 from an 81-piece set, between half-round jaws in a holder.
Is a ring gage better than gage blocks for setting a bore gage?
A ring gage of the exact size is quicker and matches the round shape of a bore. Gage blocks with jaws cover any size your set can build, so you don't need a ring for every bore.
How do I find the true zero when setting a bore gage?
Rock the gage across the gap and note the turning point of the needle. That minimum reading is the true size. Zero the dial there.
Is there a free gage block calculator for bore sizes?
Yes. The Gage Block Calculator at gageblockcalc.com finds the fewest-block stack for any bore size in inch or metric sets. Free, no login.
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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.