Using the outside micrometer

Hold the outside micrometer in your right hand with the frame in your palm and your third or little finger inside the frame. Use your thumb and forefinger to turn the thimble.

Hold the workpiece in your left hand. Turn the thimble down until a light contact is made between the anvil and spindle. If the micrometer has a ratchet stop, you may use it to obtain the correct feel or pressure. The ratchet should be clicked just once or twice for a correct reading. Moving the workpiece slightly between anvil and spindle helps square and align it. At the same time, it tells you if the feel is correct.

You may want to tighten the locknut before reading the mike; however, this is not necessary unless you want to keep the setting so you can lift it off the workpiece or hand it to another person. If so, remove your thumb and forefinger from the thimble, without disturbing it, and tighten the locknut slightly. You can then remove the micrometer from the workpiece.

When using larger outside micrometers, hold the frame in your left hand and locate the anvil against the workpiece. Holding the micrometer square, turn the thimble with the thumb and forefinger of your right hand. Move the micrometer slightly to the left and right as you turn the thimble. This will help you align or square the micrometer correctly on the workpiece.

Sometimes the workpiece may be attached to a large machine or too heavy to hold in your hand; a second person may be needed to assist with large micrometers.

The vernier micrometer is used when it is necessary to obtain greater accuracy; this micrometer reads to ten-thousandths of an inch.

This micrometer has an additional scale called a vernier scale, which makes it possible to read the number of ten-thousandths when the thimble lines do not coincide exactly with the index line. The vernier is located at the back of the sleeve.

There are 10 lines, numbered from 0 to 9, each of which represents 0.0001 inch (one ten-thousandth). This is equal to one-thousandth divided into 10 parts.

When a line on the thimble does not line up exactly with the index line on the sleeve, look at the vernier. Find the numbered line of the vernier that lines up or coincides exactly with any line on the thimble. This will be the number of ten-thousandths to be added to the reading in thousandths.

Click on image to enlarge.

Reading a Vernier Micrometer