Inspection method · DIM
Dimensional measurement
The right instrument for each tolerance. Dimensional measurement is only as good as the method's resolution, uncertainty and the inspector's technique.
01How it works
Dimensional measurement uses contact instruments (calipers, micrometers, bore gauges, dial indicators, height gauges), attribute gauges (plug, ring and thread gauges, go and no-go gauges), surface plates and fixtures, and optical devices.
A practical rule is that measurement uncertainty should be a small fraction of the tolerance, often 10% or less. Calibration status, temperature and the measurement method all contribute.
02Typical industrial applications
- Machined diameters and lengths
- Thread verification
- Hole positions with fixtures
- Weld and fabrication dimensions
- Sheet metal parts
- Incoming inspection
03Benefits and what it detects
- Fast and flexible
- Portable
- Suitable for most production tolerances
- Immediate results
04Limitations
- Complex GD&T requires CMM or fixtures
- Operator technique affects results
- Temperature effects on tight tolerances
- Attribute gauges give no measured value
| Instrument | Typical resolution | Suited for tolerances of |
|---|---|---|
| Vernier or digital caliper | 0.01 mm | ±0.1 mm and wider |
| Outside micrometer | 0.001 mm | ±0.01 mm and wider |
| Bore gauge | 0.001 mm | IT7 bores and wider |
| Height gauge on surface plate | 0.01 mm | ±0.05 mm and wider |
| Plug and ring gauges | Attribute | Specified limits |
05Specifying and reviewing the method
Specify critical characteristics, measurement method where it matters (for example two point versus least squares diameter), and the required report format. The tolerance calculator helps evaluate limits.
Other references: ISO 14253-1 (decision rules for conformity), ISO 286 (ISO tolerance system)