The Micrometer - 4: Thimble
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WARNING: Machine tools present a safety hazard. Improper operation can result in severe injury. These topics are for non-laboratory study only and are not to be used in conjunction with the operation of any tool or machine described herein. Never use a machine tool without the supervision of a qualified instructor.
The thimble is permanently attached to the spindle which fixes the two as a single assembly. Therefore it is important to recognize that rotating the thimble also rotates the spindle and thereby moves the assembly in and out in relation to the frame (the frame is threaded like a nut to fit the spindle).

The thimble can be a solid piece with a knurl gripping surface or in two parts with a friction thimble that slips when the mike is clamped lightly between the anvil and spindle. Some micrometers, in place of a friction thimble, have a rachet on the end of the thimble that also slips when clamped lightly.

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label: micrometer, history, anvil, thimble, spindle, frame, barrel, ratchet, adjustment, holding, handling, reading, vernier