What are the parts of a micrometer?
The micrometer is a tool used for obtaining highly accurate measurements. Micrometers typically have two measurement scales: metric and imperial.
A micrometers metric measurements increase in increments of 0.01mm, whilst the imperial measurements increase in increments of 0.001 inches.
Micrometer Measuring Faces
Objects to be measured are placed between the measuring faces; the anvil and the spindle.
The anvil is the stationary measuring face against which parts are held until the spindle makes contact with the work.
The threaded spindle is the moving measuring face of the micrometer.
Micrometer Sleeve Scale
The scale on the sleeve of the micrometer is the instrument’s primary measuring scale.
Together with the thimble scale, the sleeve scale displays the measurement taken.
Micrometer Thimble Scale
The secondary measuring scale, the thimble scale, provides the two remaining significant figures of a measurement.
This part of the measurement is the value on the scale that aligns with the index line on the sleeve scale.
Micrometer Index Line
The index line, which runs along the sleeve of the micrometer, is used to indicate the value shown on the thimble scale.
When the thimble is turned, the spindle rotates and alters the distance between the measuring faces of the micrometer.
Some micrometer thimbles incorporate a friction drive. This allows for a more accurate reading, particularly when used by the inexperienced user.
Micrometer Ratchet Speeder
The ratchet speeder increases the speed at which the spindle rotates, so the space between the anvil and the spindle is reduced more quickly than it would be if the thimble were used.
Using the ratchet speeder reduces the time it takes to use the micrometer.
The ratchet incorporates a slipping clutch mechanism that prevents over-tightening and aids the user to apply a constant measuring force to the spindle, helping to ensure reliable measurements.
Micrometer Locking Device
The locking device secures the spindle and preserves the measurement so that the micrometer can be removed from the workpiece before taking the reading.
Some micrometers have a lock nut (as shown), whilst others may have a locking lever (see image).
The u-shaped frame is designed to be rigid and stable. It supports the anvil and the sleeve of the micrometer.
The frame is held by the user whilst measurements are taken.