How to Read a Micrometer

Jefferson College

Area Technical School

Applied Mathematics

The Micrometer

• A micrometer generally provides greater precision than a caliper, but can measure a smaller range of lengths.

Parts of a Micrometer

• A standard outside micrometer has a U-shaped frame, an anvil, a spindle, a sleeve or barrel, and a thimble

To use a Micrometer…

• Place the object to be measured in the opening and turn the thimble until the spindle contacts the work.

• Use the ratchet stop to apply a consistent pressure to the part.

• Use the clamp ring to hold the thimble in place while you read the micrometer.

To read the Micrometer…

• Read the exposed number on the barrel 0,1,2,3,4,5,6,7,8,9. Each of these division represents 0.100 inch.

• Read the number of divisions past the number. Each of these division represents 0.025 inch.

• Read the division on the spindle. These usually read to one thousandth of an inch.

…cont

• Each of the 25 marks on the thimble represents 0.001 inch. Each complete turn on the thimble equals 0.025 inch.

• Each division on the sleeve is equal to 0.025 inch. Four divisions are equal to 0.100 inch (4 x 0.025 = 0.100).

• Therefore, four complete rotations of the thimble will equal 0.100 inch.

• Note the number of lines on the sleeve that are exposed, starting with zero.

• Count the number of 0.100 lines that show.

• Add to this the value of the 0.025 lines such as 0.025, 0.050, or 0.075.

…cont

• To this reading, add the number of divisions on the thimble from zero to the line that coincides with the index line on the sleeve.

• The index line is the long line that runs lengthwise to the sleeve. All thimble readings are taken from the line on the thimble that lines up with this index line.

Example 1

The last large Number is 1 so we have .100we have two lines past the 2 so we have .050and the thimble is turned to the 0 so we have 0add it together and we have .150

Example 2

The last large Number is 2 so we have .200we have two lines past the 2 so we have .050and the thimble is turned to the 5 so we have .005add it together and we have .255

Example 3

The last large Number is 2 so we have .200we have two lines past the 0 so we have 0and the thimble is turned to the 19 so we have .019add it together and we have .219