READING THE MICROMETERS
To use these you must understand that the pitch of the screw thread on the spindle of a micrometer is
1/40" Or 40 threads per inch. So one complete revolution of the thimble advances the spindle face
toward or away from the anvil face 1/40" or .025."
On the longitudinal line on the sleeve it is divided into 40 equal parts by vertical lines that correspond to
the number of threads cut on the spindle. On the spindle each vertical line designates 1/40" or .025"
and every fourth line designates .100." You will see that the line marked "1" will represents .100," the
line marked "2" will represents .200" and so on.
The beveled edge of the thimble is divided into 25 equal parts with each line representing .001" and
every line numbered consecutively. By rotating the thimble to the next higher line moves the spindle 1/25
of .025" or .001." Twenty-five divisions shows a complete revolution, .025" or 1/40."
What would be the answer if the reading if the edge of the thimble is between the .125" and the .150"
lines, and the line on the thimble is the coinciding line? The answer is: Micrometer reading = sleeve +
thimble or .125 + .015 = .140 of an inch.