External Micrometer is also known as Outside Micrometer or External Micrometer.
It is used to check outside diameter of circle by the means of accuracy of 0.01 mm or up to 0.001 mm.
Vernier type Micrometer gives highest acceptable accuracy of 1 micron such gauge is vernier type micrometer.
How to Measure with Micrometer?
According to above figure, the last unit of main scale is 8 mm. Bottom scale has a span of 0.50 mm,if we see this graduation we have to be added 0.50mm to actual reading.
The second scale is the rotational scale with a number of 0 to 50. Each number show digit after dot point. For instance 0.46 mm appear at the matching line.
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So,our total reading is 8.96 mm
The accuracy of External Micrometer 0.01 mm which is very acceptable, accurate and precise .
There is another kind of micrometer available called vernier micrometer, which also gives an accuracy of 0.001 mm. Digital and External(Analog) both Micrometer follow national or international measurement standards by the mean of its unit is mm or inches.
The cost of a Digital Micrometer is a little bit higher than the External type. If we think cost related to the accuracy, that is fair enough. Cost may vary brands to brands, usually depend upon the quality of material and technology used.
You can choose Digital Micrometer with an accuracy up to 0.001 mm, if cost does not matter.
Some most famous Brands which are known for their quality promise available in a market like Mitutoyo, Baker etc.