A micrometer is used to make precise measurements to the thousandth of an inch.
Parts of an Inch Micrometer
Sleeve:
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.
Thimble:
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
Reading Example:
- 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,
indicating .025″. - 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.
