Operation of Micrometer Screw Gauge SOP



  • To provide a procedure for Operation of Micrometer Screw Gauge.

2.0 SCOPE :

  • This procedure is applicable to Micrometer Screw Gauge.


  • Quality control Chemist and above


  • Quality Control Head


  • Micrometer Screw Gauge is made up of a main scale and a thimble scale and it is used for measuring the thickness of packaging materials like cartons, aluminum foil etc.
  • It can measure maximum thickness of 25.0 mm.
  • The thimble has a total of 50 markings representing 0.50 mm.
  • The smallest marking is 1 mm on the main scale (sleeve) and 0.01 mm on the thimble scale (thimble).
  • Least count of Micrometer Screw Gauge is 0.01 mm.


  • Set the 0 by gently moving the thimble.
  • In case it is not zero, then instrument has zero error which is be adjusted.
  • Put the object between the fix rod and movable rod and fix the object between two rods gently moving the screw.
  • Spin the movable rod clockwise until the spindle just meets the object.
  • Set the lock nut while the micrometer is still on the object to fix the position.
  • Note down the reading of scale as below:
    • The first part is contributed by the main scale on the sleeve.
    • To obtain the first part of the measurement: Look at the image image (b) you will see a number 5 to the immediate left of the thimble.
    • This means 5.0 mm. Notice that there is an extra line below the datum line, this represents an additional 0.5 mm. So the first part of the measurement is 5.0 + 0.5 =5.5.
    • The second part is contributed by the rotating vernier scale on the thimble.
      • To obtain the second part of the measurement: Look at the image image (b), the number 28 on the rotating vernier scale coincides with the datum line on the sleeve.
      • Hence, 0.28 mm is the second part of the measurement.
    • You just have to add the first part and second part of the measurement to obtain the micrometer reading,
      • i.e.,  5.5 + 0.28 = 5.78.
    • Remove the object from the micrometer.
    • Reset the lock nut to the unlock position.
    • Keep the instrument in box after use.
    • Calibration of Micrometer Screw Gauge is perform by approved outside agency on  yearly basis.

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