Inspection and GD&T
Gage block stack calculator
Clear the rightmost digit first; 2.6843 in is 0.1003 + 0.134 + 0.450 + 2.000, four blocks.
Technical review pending. Formulas and values are cited. This notice comes down after a machinist review.
Blocks in the stack
blocks
Stack = 0.1003 + 0.134 + 0.450 + 2.000 = 2.6843 in
Sum check matches the 2.6843 in target. 81-piece inch set.
| Block | Size (in) | Clears | Remainder (in) |
|---|---|---|---|
| 1 | 0.1003 | the 0.0001 in digit | 2.5840 |
| 2 | 0.134 | down to a 0.050 in step | 2.4500 |
| 3 | 0.450 | down to whole inches | 2.0000 |
| 4 | 2.000 | whole inches | 0.0000 |
Source: Machinery's Handbook (gage blocks). Set contents from common 81-piece and metric set lists; check your set's chart
How it works
Work from the rightmost digit to the left and subtract after every block. Each step uses the one series that can clear the digit in front of you, so the stack ends up with the fewest blocks the set allows.
- Take the block that clears the last digit (the 0.1001 to 0.1009 in series on an inch set).
- Take the 0.101 to 0.149 in block that leaves a multiple of 0.050 in.
- Take the 0.050 to 0.950 in block that leaves whole inches.
- Finish with the 1, 2, 3 and 4 in blocks.
Worked example: 2.6843 in from an 81-piece set
Build 2.6843 in.
- 0.1003 clears the 3: 2.6843 - 0.1003 = 2.5840 in.
- 0.134 leaves a 0.050 step: 2.5840 - 0.134 = 2.4500 in.
- 0.450 leaves whole inches: 2.4500 - 0.450 = 2.0000 in.
- 2.000 finishes it: 2.0000 - 2.000 = 0.
Result: 0.1003 + 0.134 + 0.450 + 2.000 = 2.6843 in, four blocks.
Worked example: 1.0396 in for a sine bar
The stack for 12° on a 5 in sine bar is 1.0396 in.
- 0.1006 clears the 6: 1.0396 - 0.1006 = 0.9390 in.
- 0.139 leaves a 0.050 step: 0.9390 - 0.139 = 0.8000 in.
- 0.800 finishes it: 0.8000 - 0.800 = 0.
Result: 0.1006 + 0.139 + 0.800 = 1.0396 in, three blocks.
Worked example: 41.785 mm from a 112-piece set
Build 41.785 mm.
- 1.005 clears the 5: 41.785 - 1.005 = 40.780 mm.
- 1.28 leaves a 0.5 mm step: 40.780 - 1.28 = 39.500 mm.
- 14.5 leaves a 25 mm step: 39.500 - 14.5 = 25.000 mm.
- 25 finishes it: 25.000 - 25 = 0.
Result: 1.005 + 1.28 + 14.5 + 25 = 41.785 mm, four blocks.
| Set | Sizes | Step | Blocks |
|---|---|---|---|
| 81-piece inch set | 0.1001 to 0.1009 in | 0.0001 in | 9 |
| 81-piece inch set | 0.101 to 0.149 in | 0.001 in | 49 |
| 81-piece inch set | 0.050 to 0.950 in | 0.050 in | 19 |
| 81-piece inch set | 1.000, 2.000, 3.000, 4.000 in | 1.000 in | 4 |
| 112-piece metric set | 1.0005 mm | single block | 1 |
| 112-piece metric set | 1.001 to 1.009 mm | 0.001 mm | 9 |
| 112-piece metric set | 1.01 to 1.49 mm | 0.01 mm | 49 |
| 112-piece metric set | 0.5 to 24.5 mm | 0.5 mm | 49 |
| 112-piece metric set | 25, 50, 75, 100 mm | 25 mm | 4 |
| 87-piece metric set | 1.001 to 1.009 mm | 0.001 mm | 9 |
| 87-piece metric set | 1.01 to 1.49 mm | 0.01 mm | 49 |
| 87-piece metric set | 0.5 to 9.5 mm | 0.5 mm | 19 |
| 87-piece metric set | 10 to 100 mm | 10 mm | 10 |
Totals: 81, 112 and 87 blocks. Sets from different makers vary; check the chart in your set's case.
Shop notes
- Wear blocks go on the ends. The calculator subtracts both before it picks the rest.
- Sizes under 0.1001 in (or 1.0005 mm) need a special block.
- Wring clean blocks and let them reach room temperature before you trust the stack.
- Grade and calibration set the accuracy of the stack, not the arithmetic.
FAQ
How do you build a 1.0396 in stack?
From an 81-piece set: 0.1006 + 0.139 + 0.800 = 1.0396 in, three blocks. That is the stack for 12° on a 5 in sine bar.
Why start with the last digit?
Only one block can clear it: for 2.6843 in, the 0.1003 in block is the only one that ends in 3. Working right to left keeps the block count low.
What is in an 81-piece set?
Nine blocks from 0.1001 to 0.1009 in, 49 blocks from 0.101 to 0.149 in, 19 blocks from 0.050 to 0.950 in, and 1, 2, 3 and 4 in blocks.
Is a single gage block worth it for a home shop?
A single calibrated block checks micrometers. A full set is for building sine bar and height setups.
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