To read a micrometer accurately, follow these steps:
- Read the Sleeve Measurement
Look at the horizontal scale on the sleeve of the micrometer. This scale shows measurements in increments of 0.025 inches (25 thousandths) and also marks every tenth of an inch (0.1"). Count the visible lines and note the last fully visible number or line to get the base measurement
- Read the Thimble Measurement
The thimble is the rotating part with a scale typically divided into 25 or 50 increments. Each increment represents 0.001 inch (one thousandth). Read the number on the thimble that aligns with the horizontal reference line on the sleeve. Add this to the sleeve measurement
- Read the Vernier Scale (if present)
Some micrometers have a vernier scale on the thimble for extra precision, showing ten-thousandths of an inch (0.0001"). Identify the vernier line that aligns best with a line on the thimble scale and add this value to the previous total
- Add the Measurements Together
Combine the sleeve reading with the thimble reading, then append the vernier reading if available. For example, if the sleeve reads 0.100", the thimble reads 0.023", and the vernier reads 0.0004", the total measurement is 0.1234"
Summary of Reading a Micrometer
Step| What to Read| Typical Scale Increment| How to Use It
---|---|---|---
Sleeve| Main horizontal scale| 0.025" and 0.1" increments| Base measurement
Thimble| Rotating scale| 0.001" increments| Add to sleeve reading
Vernier (optional)| Small scale on thimble| 0.0001" increments| Add for extra
precision
Important Tips
- Always add the thimble reading to the sleeve reading.
- For the vernier, do not treat the number as a simple decimal addition; place it in the ten-thousandths position.
- When reading the thimble, if the line falls between two numbers, always take the lower number
This method works for both imperial and metric micrometers, though metric versions use millimeters and fractions thereof
. By following these steps, you can accurately read measurements down to a thousandth or even ten-thousandth of an inch, depending on your micrometer's precision
