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How to Use a V-Block with Gage Blocks
Guide · Updated October 27, 2026
V-blocks hold round work square to the surface plate. Combine one with gage blocks and you can find a part's center height, scribe center lines and set an indicator without guessing. It only takes one constant for a 90° V.
Center heights, built for you
The free Gage Block Calculator finds the fewest-block stack for any height. Free, no login.
The 90° V-block constants
- Center above apex: 0.7071 × D (D ÷ 2 ÷ sin 45°)
- Top of part above apex: 1.2071 × D
Worked examples (apex height 1.000 in)
| Part dia. | Center height | 81-piece stack |
|---|---|---|
| 1.000 in | 1.7071 in | 1.000 + 0.500 + 0.107 + 0.1001 |
| 0.500 in | 1.3536 in | 1.000 + 0.150 + 0.103 + 0.1006 |
| 2.000 in | 2.4142 in | 2.000 + 0.200 + 0.114 + 0.1002 |
Use your V-block's real apex height. Center heights are rounded to 0.0001 in.
Step by step
- Know the apex height: Find the V-block's apex height, the distance from the base to where the V faces would meet.
- Calculate center height: Center height = apex height + 0.7071 × D for a 90° V.
- Build the stack: Build the fewest-block stack for that height.
- Set the height gage: Zero a height gage or test indicator on the stack.
- Transfer to the part: Set the part in the V-block and check or scribe at the center line.
Tips
- Use matched pairs of V-blocks for long parts, and clamp them lightly.
- Clean the V faces. A chip lifts the part by many times its own size.
- For angles, see sine bars. For height setting, see checking a height gage.
FAQ
How high does a round part sit in a 90° V-block?
The center sits 0.7071 × D above the V apex, and the top of the part sits 1.2071 × D above the apex. A 1.000 in pin has its center 0.7071 in above the apex.
How do I find the center height of a part in a V-block?
Add the V-block's apex height (from its certificate or your measurement) to 0.7071 × D. Build that height in gage blocks to set a height gage or test indicator.
What stack sets the center of a 1 inch pin in a V-block with a 1.000 inch apex height?
1.000 + 0.7071 = 1.7071 in. From an 81-piece set: 1.000 + 0.500 + 0.107 + 0.1001.
Can I check roundness in a V-block?
A V-block with an indicator shows lobing that a micrometer can miss, but the reading isn't a direct roundness value. For a true roundness check, use centers or a roundness instrument.
Is there a free calculator for the stack?
Yes. The Gage Block Calculator at gageblockcalc.com builds the stack for any center height in inch or metric sets. Free, no login.
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Questions? Ask a machinist.
General shop information only — follow your gage manufacturer's instructions and your quality system.