DICK LURIA / SCIENCE PHOTO LIBRARY. DICK LURIA / SCIENCE PHOTO LIBRARY.
Detail of a micrometer screw gauge in use here to check standard external diameters on metal tubing. A reading is taken by turning the thimble (area held by fingers) until the object is gripped between the jaws of the gauge, called the spindle (forward jaw) & anvil (distant). The scale nearest the frame of the gauge, called the sleeve, is in quartre millimetres. Fractions of a turn are indicated on the thimble (held by fingers), which has a scale of 50 equal divisions. The instrument is used for measuring small distances.
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