are devices for measuring linear dimensions:
The conventional micrometer
has a thimble that rotates on a barrel.
The thimble drives a screw that opens or
closes the micrometer:
One full turn of the thimble
changes the measured dimension by 0.025".
There is a scale along the barrel divided
into intervals of 0.025", thus a complete
turn of the barrel will cause a one increment
movement. There are also 25 equi-spaced
reference marks on the thimble, moving one
increment of these marks changes the measurement
For other devices see