To lay down a procedure for Operation and calibration of micrometer screw.


This procedure is applicable for Operation and calibration of micrometer screw



MICROMETER SCREW: A Micrometer is a measuring device used for taking the exact measurement of an object. It is also known as micrometer screw gauge.


mm :  millimeter


QA Department Person:

To used instrument as per defined procedure



Before use ensure that instrument is calibrated.

Cleaning Procedure

Clean the Micrometer screw before & after each use.

Clean the Micrometer screw with the help of dry, clean, lint free cloth.

Operating Procedure

Diagram of an External Micrometer


Keep the micrometer in stable room temperature before starting the measuring process. Check Zero error before measurement & adjust if necessary.

Hold the micrometer from its heat isolation plate.

Rotate the ratchet anticlockwise allowing sufficient space between the anvil and the spindle to accommodate the object to be measured.

Place the object to be measured between the anvil and the spindle.

Spin the ratchet clockwise until the spindle just meets the object.

Keep spinning the ratchet gently until 3 clicks are heard.

Check that both the anvil and the spindle are touching the object evenly.

Set the lock nut while the micrometer is still on the object.

Remove the object from the micrometer.

Read off the value from the Sleeve scale to obtain reading to the nearest half millimeter.

Read off the value from the thimble scale that is parallel with the reference line of the Sleeve scale.

Add both values obtained from And to obtain the total measurement reading.

  • Micrometer reading example:

Thimble scale reads = 0.35mm

Total Measurement = 16.35mm

With Vernier scale

Sleeve scale reads =   6.00mm

Thimble scale reads = 0.21mm

Vernier scale reads =  .003mm

Total Measurement =   6.213mm

Reset the lock nut to the unlock position.

Turn the ratchet clockwise to slightly close the micrometer prior to its storage.

Calibration Frequency

Calibration shall be performed by outside agency.

Calibration Frequency: Yearly (± 30 Days)


Inspect the micrometer for any signs of damage, such as indications that it might have been dropped.

Check that both spindle and anvil tips are flat, free from scratches, dents and chipped edges.

Move the thimble through its entire range (i.e. 25mm) to check that it moves smoothly.

Perform the zero point alignment test (see 6.3.5).

To clean the tips of the anvil and the spindle:

Rub off any visible dirt, dust and grit with a lint free cloth.

Close the micrometer all the way with a piece of paper clamped in between.

Pull the paper out whilst rubbing the tips of the spindle and the anvil clean.


The micrometer is a highly heat sensitive instrument and should be stored at room temperature.

Hold the micrometer from its heat isolation plate whilst handling to prevent heat transfer from hand of user to the micrometer.

The object to be measured should also be kept at room temperature since this may also affect the reading.

Do not over tighten the micrometer as this can lead to deformation of both the anvil and spindle and the object being measured.

Store the micrometer in its appropriate storage compartment to prevent any wearing of the anvil and/or spindle.

Store the micrometer with the anvil and spindle not in contact with each other so that any temperature fluctuations will not stress the instrument.

Measure the desired object a number times to ensure that the reading obtained is accurate.

Do not operate abruptly, drop or strike the micrometer.