Choosing an Outside Micrometer: Range, Resolution, DIN 863

How does an outside micrometer work?

An outside micrometer measures external dimensions through a precision spindle with a 0.5 mm thread pitch. One turn of the thimble moves the spindle exactly 0.5 mm, divided into 50 graduations. This gives a direct reading of 0.01 mm.

The workpiece is held between the fixed anvil and the moving spindle. The rigid C-shaped frame keeps both measuring faces exactly parallel and absorbs the measuring force without deforming.

• Anvil: fixed measuring face in the frame.
• Spindle: moving face with a 0.5 mm thread pitch.
• Sleeve and thimble: reading in mm and 0.01 mm.
• Ratchet: applies a constant measuring force.
• Locking lever: fixes the measured value.

Which range and resolution do I need?

Each micrometer frame covers only 25 mm: 0‑25, 25‑50, 50‑75, 75‑100 mm and so on. For a wider span you need either several instruments or a set with interchangeable anvils. Choose the range to match your largest and smallest workpiece.

Analog models with a vernier resolve down to 0.001 mm but are slower to read. Digital micrometers show 0.001 mm directly, switch between mm and inch and send readings to the analysis system through a data interface.

What does DIN 863 require for accuracy?

The DIN 863 series defines the design and permissible error limits for outside micrometers. It sets the maximum permissible measurement deviation, the flatness of the measuring faces and the parallelism of anvil and spindle. Only then are readings comparable and traceable.

• Check the zero point before each series with the setting standard and adjust via the sleeve.
• For ranges from 25 mm up, use the supplied setting ring or a gauge block.
• Document calibration with parallel gauge blocks to DIN EN ISO 3650.
• Measure at a reference temperature of 20 °C and let workpiece and instrument settle.

How do I measure and maintain it correctly?

For a repeatable reading, always close the micrometer using the ratchet until it slips two or three times. This applies the same measuring force every time so the result does not depend on feel. Use the locking lever to fix the value before reading.

• Place the workpiece burr-free and clean between the faces.
• Never force the thimble closed, only use the ratchet.
• Store with faces slightly open to avoid point corrosion.
• Keep the instrument oil-free and dust-free in its case.

Frequently asked questions