A micrometer is a device designed for measuring linear dimensions using the absolute contact method in the area of small dimensions with high accuracy (from 0.01 to 0.001 mm), the conversion mechanism of which is a screw-nut micropair.
It is necessary to keep the micrometer clean. Be careful not to drop the micrometer, as its clip may become deformed, resulting in inaccurate measurements.
The operation of the micrometer is based on the movement of the screw along the axis when it rotates in a fixed nut. The displacement is proportional to the angle of rotation of the screw around the axis. Full revolutions are counted on a scale printed on the stem of the micrometer, and fractions of a revolution are counted on a circular scale printed on the drum. The optimal movement of the screw in the nut is only a length of no more than 25 mm due to the difficulty of producing a screw with an accurate pitch over a greater length. Therefore, micrometers are manufactured in several standard sizes for measuring lengths from 0 to 25 mm, from 25 to 50 mm, etc. For micrometers with measurement limits from 0 to 25 mm, with the closed measuring planes of the heel and the micrometer screw, the zero mark of the drum scale must exactly coincide with the longitudinal mark on the stem, and the beveled edge of the drum - with the zero mark of the stem scale. For measuring lengths greater than 25 mm, a micrometer with replaceable anvils is used; setting such micrometers to zero is done using a setting measure applied to the micrometer or end measures. The product being measured is clamped between the measuring planes of the micrometer. Typically, the screw pitch is 0.5 or 1 mm, and the scale on the stem has divisions of 0.5 or 1 mm, respectively, and the drum is marked with 50 or 100 divisions to obtain a reading of 0.01 mm. This reading is the most common, but micrometers with readings of 0.005, 0.002, and 0.001 mm are also available. A constant axial force is maintained when the screw contacts the workpiece using a friction device called a ratchet. When the micrometer's measuring surfaces are in close contact with the surface of the workpiece, the ratchet begins to rotate with a slight clicking sound. The micrometer should stop rotating after three clicks.
[The text is based on materials from the website: «BMWman»]