Reading a Metric Micrometer

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TM 9-243 READING A METRIC MICROMETER The same principle is applied in reading the metric graduated micrometer, but the following changes in graduations are used: The pitch of the micrometer screw is 0.05 mm. One revolution of the spindle advances or withdraws the screw a distance equal to 0.5 mm. The barrel (1) is graduated in millimeters from 0 to 25. It takes two revolutions of the spindle to move the barrel 1 mm. The thimble (2) is graduated in 50 divisions with every fifth line being numbered. Rotating the thimble from one graduation to the next moves the spindle 1/50 of 0.5 mm, or 1/100 mm. Two graduations equal 2/100 mm, and so forth. CARE OF MICROMETERS TO READ MEASUREMENT AS SHOWN ABOVE: Read highest figure visible on barrel (1) . . . . . . . . . . . . . . 20 = 20.0 mm Number of lines visible between the No. 20 and thimble edge (2) . . . . . . . . . . . . . . . . . . .2 = 2.0 mm The line on the thimble that coincides with or has passed the revolution or long line in the barrel (3) . . . . . . . . . . . 36=36/100 (.36) mm NOTE Remember that 1 revolution is 0.5 mm. It takes 2 revolutions to move 1 mm. Measurement reading . . . . . . . . . . . TOTAL 22.36 mm 1. Coat metal parts of all micrometers with a light coat 3. Keep graduations and markings on all micrometers of oil to prevent rust. clean and legible. 2. Store micrometers in separate containers provided 4. Do not drop any micrometer. Small nicks or by manufacturer. scratchescan cause inaccurate measurements. 7-6

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