Roll down until the end of the page, drag and drop the spindle of bigger visualization in teh vertical for fine aproximation or the spindle of smaller visualization in teh vertical for fast advance.
The resolution of micrometer is obtained of the interaction of the 'thread of micrometer' with the 'internal plug'. The thread of micrometer has your step of 0.025in. This means that a complete turn (360°) of the spindle will produce an advance of twenty five thousandths of inch.
The decimal reading of this instrument is obtained from vertical marks of the sleeve. This way, the number three represents 0.3".
The milesimal reading is obtained because of the spindle perimeter, where are written twenty five divisions equidistants. A complete turn will produce an advance of 0.025" and the divisions will pass trough the 'refference line'.
The reading in tenths of thousandth is obtained applying the principle of the Vernier scale reading, by marks written in the thread.
Frame, sleeve, thimble, reading line, fuse, meause faces, lock nut and ratchet are some of the components of the micrometer <- to know better them clic here.