Using tips for micrometers

Micrometers are the most commonly used variable-reading hand tools for checking lengths and outside diameters on the shop floor. They can also be used for checking gear threads, depths and grooves. The most common type incorporates two basic scales: the linear scale, which measures directly the axial advancement of the spindle (usually identical to the pitch of the micrometer screw), and the circumferential (vernier) scale, which indicates the amount of partial rotation applied to the barrel.
The micrometer is a contact instrument. Sufficient torque must be applied to the micrometer to make good positive contact between the part and the instrument. The only torque calibration in the human hand is the operator's "feel." What feels like solid contact to one operator may not feel correct to another, so the readings will be different. To eliminate the "feel" aspect of the measurement, micrometer designers incorporate a ratchet or friction thimble mechanism as an attempt to ensure more consistent contact pressure and eliminate the human influence, achieving more consistent gaging pressure.