Micrometer accuracy is model-specific. Two tools can display the same resolution but have different permissible error, measuring ranges or geometric specifications. This table covers selected Mitutoyo Coolant-Proof Series 293 digital micrometers. Use the model number to match each specification to the actual instrument; do not treat the table as a universal production tolerance for all metric micrometers.

Metric micrometer accuracy tolerances

Accuracy, resolution and measuring faces

Resolution describes the smallest displayed increment. Accuracy is the manufacturer’s stated permissible indication error under the specified conditions. A 0.001 mm display step does not mean the tool is accurate to 0.001 mm, nor does it prove the measurement uncertainty of a particular inspection. The Series 293 models in the table show different manufacturer accuracy limits across range groups even though many share 0.001 mm resolution.

Flatness and parallelism are separate measuring-face characteristics. Mitutoyo lists them independently because a micrometer can have an acceptable indication error while its anvils still require their own geometry checks. These specifications are stated in micrometres and should not be confused with the resolution or overall accuracy field. Keep the units visible when comparing product models.

How range affects model choice

Choose a measuring range that contains the workpiece dimension. For example, a 0–25 mm model and a 25–50 mm model cover different intervals and have their own accuracy lines. Larger models in this series extend to 300 mm, and the manufacturer’s listed accuracy increases from ±1 µm for selected smaller ranges to ±4 µm for 250–300 mm models. Do not extrapolate an accuracy figure to an unlisted range or assume a model suffix is interchangeable with another.

The source also distinguishes ratchet-stop and ratchet-thimble variants. Their measuring force and other features may differ even where the range and accuracy look similar. The model number is therefore the reliable lookup key. Verify the exact instrument label, resolution setting, measuring force and product sheet before putting a value into an inspection plan.

Using accuracy in inspection

Instrument accuracy is only one part of a measurement decision. The calibration status, master standards, temperature, workpiece and tool thermal state, cleanliness, contact force, alignment, operator technique and repeatability all contribute. A published accuracy value is not a calibration certificate, a traceability statement or a complete measurement uncertainty budget.

For a tolerance decision, compare the measurement system capability and uncertainty with the drawing tolerance and quality procedure. If the tolerance is close to the micrometer’s stated accuracy, use an appropriate calibration and decision rule rather than treating the displayed digits as definitive. Set the micrometer to zero using the supplied or specified standard when required, keep the anvils clean, and use the ratchet consistently.

Limits of this table

This is a selected model list from one Mitutoyo product family. Other mechanical or digital micrometers, high-accuracy instruments and models from different manufacturers have different specifications. The listed ranges are not manufacturing tolerances for parts. A part’s allowable size comes from its engineering drawing and governing standard; the instrument specifications describe the tool used to measure it.

Before an audit or acceptance check, consult the current page and documentation for the exact order number. Confirm whether the tool is metric-only or dual-unit, and retain the original units and precision. If the instrument model is not listed here, do not borrow a neighboring model’s accuracy value.

The table expresses accuracy limits in millimetres so metric-only and dual-unit models can be compared in one unit. Values displayed as 0.001 mm represent a stated ±1 µm limit, and values converted from the manufacturer’s inch specification retain the exact millimetre conversion. The positive number in the dataset is the magnitude of the limit; the plus/minus meaning is explained here. This conversion does not add precision to the instrument or change the manufacturer’s guarantee.