How to Read Measuremements on an Outside Micrometer

Outside micrometers are devices used to measure the diameter of a cylinder, sphere, or other round object with a very high degree of accuracy and are made in both metric and English units. The handle of the micrometer holds a shaft, or spindle, that is advanced and retracted by twisting the handle. The screw threads are precisely machined, so when the spindle is advanced enough that the object being measured is pressed against the anvil, an accurate measurement can be read on the micrometer's gauge.

Things You'll Need

• Item to measure Outside Micrometer

Instructions

1. Place the object to be measured in the micrometer and twist the handle until it can be held in place between the spindle and the anvil. The object should be snug but not overtightened.

2. Read the linear gauge along the shaft. This will be different depending on the accuracy and units being measured. Usually, this gauge will be abbreviated so that "2" is actually "0.2 inches" for English units and "2.4" would be "0.24 mm" for metric units.

3. Read the gauge on the barrel using the axial line on the linear gauge. The markings on the barrel will vary, depending on the accuracy of the linear gauge. A linear gauge that measures quarter-step increments will have a barrel gauge with 25 increments. Half-step linear gauges will have 50 increments on the barrel gauge. A reading of "17" on the barrel gauge would equal "0.017 inches" on an English unit micrometer.

4. 

   Combine the two readings. A reading of "2.75" on the on the linear gauge combined with a reading of "1" on the barrel gauge of an English unit outside micrometer would equal "0.276 inches."

Tips & Warnings

• Some micrometers will have an additional horizontal gauge above or below the linear gauge. This allows accurate readings to the fourth, rather than the third, decimal place.

• Micrometers are precisely machined and calibrated. Excessive heat or cold or impact from dropping them can greatly affect their accuracy. Handle micrometers with care.