Resolution is not accuracy
Resolution is the smallest step an instrument displays, e.g. 0.01 mm. Accuracy is how close the reading is to the true value. A digital caliper reading 0.01 mm is not necessarily accurate to 0.01 mm — check the maker's stated error.
A simple rule: resolution should be about one tenth of the tolerance band. A part with a total tolerance of 0.1 mm (±0.05) calls for an instrument that reads 0.01 mm.
The reference temperature for dimensional measurement is 20 °C. Parts fresh off a machine are warm and expanded — let them cool first.
Vernier calipers
The most used instrument: outside, inside and depth measurement in one tool. Common ranges are 0–150, 0–200 and 0–300 mm.
| Type | How it reads | Typical resolution |
|---|---|---|
| Vernier | Vernier scale, no battery | 0.05 or 0.02 mm |
| Dial | Needle on a dial | 0.01–0.02 mm |
| Digital | Display; some models send data to a PC | 0.01 mm |
Micrometers
Finer than calipers — 0.01 mm (mechanical) or 0.001 mm (digital) — but each covers only 25 mm, e.g. 0–25 or 25–50 mm. Use the ratchet every time for a consistent measuring force.
Dial indicators and dial test indicators
They measure difference or change rather than size — shaft run-out, flatness, or setting up a part on a machine — always on a magnetic stand.
Plunger dial indicators (e.g. 10 mm range, 0.01 mm) cover general work; lever-type test indicators (about 0.8 mm range) reach tight spots such as bore walls and are used to centre work on lathes and mills.
Height, depth and bore gauges
- Height gauge: measures height and scribes lines on a surface plate
- Depth gauge: measures the depth of holes, slots and steps
- Bore gauge: measures bores precisely with a dial indicator, zeroed on a ring gauge or micrometer first
Pin, ring, thread and gauge blocks
These don't give a reading; they check pass or fail (GO / NO-GO), which makes high-volume inspection fast.
- Pin gauges: check hole size
- Ring gauges: check shaft size and zero bore gauges
- Thread gauges: plugs for internal threads, rings for external — GO must screw in, NO-GO must not
- Gauge blocks: length standards for checking and setting other instruments, in several accuracy grades
Electrical and temperature instruments
Electrical maintenance uses multimeters, clamp meters and insulation testers; machine care uses IR thermometers and thermal cameras to find hot spots. Match an electrical meter's CAT safety rating to where you measure.
Calibration and care
- Calibrate on the interval your quality system sets — usually yearly — and after any drop or doubtful reading
- Clean the measuring faces and zero before every measurement
- Store in the case, never stacked, away from magnets and heat
- Remove batteries from digital tools you won't use for a while
Frequently asked questions
- Caliper or micrometer?
- Calipers cover a wide range and several kinds of measurement — good for general work. Micrometers are finer but cover a narrow range, for sizes that need 0.01 or 0.001 mm.
- How often should instruments be calibrated?
- Most plants calibrate yearly under their quality system (e.g. ISO 9001 or IATF 16949), and again right after a drop or a doubtful reading.
- Can you source Mitutoyo codes like 500-196-30?
- Yes — send the code. If a model is discontinued we offer the replacement, e.g. the 2046S dial indicator is now the 2046A.
Get a price on measuring tools
We source Mitutoyo, Insize, Teclock, Niigata Seiki, Fluke, Hioki and many more, exact or replacement models. Send these details on LINE.
- Model code (e.g. Mitutoyo 500-196-30) or a photo of the instrument you use now
- Range and resolution needed, e.g. 0–150 mm reading 0.01 mm
- Whether you need the maker's inspection certificate or a calibration certificate
- Quantity and the date you need it
Measuring Tools & Measuring Equipment