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How to Check a V-Block
Guide · Updated October 27, 2026
V-blocks hold round work for layout, inspection and machining. If the V isn't parallel to the base, everything set in it is off. For using one, see using a V-block with gage blocks.
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Step by step
- Clean and stone: Clean the block and stone off any burrs in the V.
- Use a precision pin: Set a ground pin or gage pin in the V.
- Check parallelism: Sweep an indicator along the top of the pin, with the block on the surface plate.
- Check the other base: Flip the block onto its side or other base and repeat.
- Compare the pair: Set both blocks of a matched pair under the same pin. The readings should match.
Typical specs
- Good blocks are about 0.0002–0.0003 in over their length.
- Mark worn blocks for rough use.
Related: using V-blocks, checking 1-2-3 blocks.
Worked example: matching a pair of V-blocks
Place a 1.0000 in ground test pin in the V of each block and measure from the surface plate to the top of the pin with a height gage or a test indicator against a gage block stack. A matched pair should read within about 0.0002 in of each other. For a 90° V, the top of a pin of diameter D sits above the bottom of the V by D/2 + D/(2 sin 45°) = D × 1.2071, so a 1.000 in pin tops out 1.2071 in above the V bottom.
Check the V is parallel to the base by sweeping the top of the pin end to end; 0.0002 in change over 4 in is good. Then check the V is centered by turning the block end for end and measuring the pin from a side face; any difference is twice the offset. Stone small burrs, especially near the clamp slots, and store pairs together with their serial marks so they stay matched.
If a pair does not match, use the pair only as a set for parts where both blocks see the same error, or have them reground together. Never mix single blocks from different pairs on a precision setup.
Quick shop check
Lay a ground 1.000 in test pin in the V and indicate along the top: readings within 0.0002 in over 4 in mean the V is parallel to the base. For a matched pair, put the same pin in each block and compare heights; a typical matched-pair spec is within about 0.0002–0.0003 in. Then flip the block onto a side and check squareness with a square and light gap.
FAQ
How do I check a V-block?
Put a precision pin in the V and indicate along it on a surface plate. Repeat on each base.
Why do matched pairs matter?
Long work bridges both blocks, so they must hold the same height.
What pin do I use?
A ground pin or gage pin that sits well below the top of the V.
How do I verify the indicator?
On gage blocks. Build any reference size free with the Gage Block Calculator at gageblockcalc.com.
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General shop information only — follow your gage manufacturer's instructions and your quality system.