What is a Screw Gauge? What is Its Pitch and Least Count? How is It Used to Measure the Thickness of a Thin Copper Wire?

A screw gauge (also known as a micrometer screw gauge) is a precision instrument used to measure the dimensions of small objects with high accuracy, such as the thickness of wires, small machine parts, or the diameter of a small cylindrical object. It uses a screw mechanism for measuring the object.

Construction:

  1. Spindle: One end of the screw gauge, which is used to hold the object.
  2. Anvil: The fixed surface that the object is placed against, opposite the spindle.
  3. Screw Thread: A calibrated screw that moves the spindle toward the anvil when the thimble is rotated.
  4. Thimble: A rotating part of the screw gauge that is marked with a scale for reading the measurement.
  5. Main Scale: A scale engraved on the barrel of the screw gauge, usually in millimeters.
  6. Vernier Scale: The scale on the thimble that allows for more precise readings than what is available on the main scale.

Pitch and Least Count:

  • Pitch refers to the distance the spindle moves when the thimble is rotated one full revolution. It is usually around 0.5 mm in many screw gauges.
  • Least Count is the smallest unit of measurement that the instrument can measure, calculated by dividing the pitch by the number of divisions on the thimble. For example, if the pitch is 0.5 mm and the thimble has 50 divisions, the least count would be: Least Count=0.5 mm50=0.01 mm

Using the Screw Gauge:

To measure the thickness of a thin copper wire, the wire is placed between the spindle and the anvil. The thimble is rotated until the wire fits snugly between the two surfaces. The reading is taken from both the main scale (which provides the whole millimeter value) and the Vernier scale (which gives the precise fraction). The total reading is the sum of both scales’ values.

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