A micrometer is used to make precise measurements to the thousandth of an inch.
Parts of an Inch Micrometer
The Micrometer sleeve is divided into forty equal parts. Each part or division is indicated by a vertical line. Each vertical line represents one-fortieth of an inch or .025″, and, each fourth line is marked by a longer line and a number which designates one hundred-thousandths.
More simply, the line marked “1” represents .100″, the line marked “2” represents .200″ and so forth.
The thimble is divided into twenty-five equal parts, and, one complete rotation of the thimble coincides with the smallest division on the sleeve. Thus, the division on the thimble is one-twenty-fifth of .025″ or .001″.
How To Read an Inch Micrometer
- Note that the thimble has stopped at a point beyond “2” on the sleeve indicating .200″ (see illustration)
- Note that one additional line is visible between the graduation numbered “2” and the edge of the thimble,
- The line numbered “1” on the thimble coincides with the center line of the sleeve. It means an additional one-thousandth of an inch.
(1) Reading on the Sleeve — .200″
(2) No. of lines between “2” and the edge of the thimble — .025″
(3) Thimble line corresponding to the centerline of the sleeve — .001″
TOTAL READING — .226″
Video Example — Reading an Inch Micrometer
This video describes how to read a micrometer that is calibrated to read to the nearest thousandth of an inch.