Lathes Page: 20
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which equals 1/o1000 inch. To read, simply multiply the marks on
barrel by 25 and add the graduations on the edge of the thimble.
typical micrometer is illustrated in figure 15 i.
LOCK NUT loe
BARREL be jIJIe W7&
THIMBLE rg t;m/e
DIAMETER OF SHAFT = .4000"+.0250"+ .0010+.0007'
FIGcUri 15.-Details of micrometer caliper.
(1) Some micrometers have a vernier scale on the frame in addi-
tion to the regular graduations so that measurements within 0.0001
inch can be taken. This arrangement is shown in figure 15 @. Mi-
crometers of this type read as follows: first, determine the number of
thousandths, as with the ordinary micrometer; then find a line on the
vernier scale that exactly coincides with one on the thimble. The nm-
ber of this line represents the number of ten-thousandths to be added
to the number of thousandths contained on the regular graduations.
The relation between the graduation of the vernier and those of the
thimble is as follows: the vernier has ten divisions which occupy the
same space as nine divisions on the thimble. The difference between
the width of a vernier division and one on the thimble is equal to one-
tenth of the space on the thimble. Therefore, a mlovelment of the
thimble-equal to the difference between the vernier and the thimble
graduation-represents 0.0001 inch.
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United States. Army. Air Corps. Lathes, book, November 29, 1940; Washington, D.C.. (digital.library.unt.edu/ark:/67531/metadc96655/m1/22/: accessed May 22, 2017), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.