What is Screw Gauge: Overview, Questions, Preparation

A screw gauge is used to measure the diameter and radius of any metal sheet. It is a U-shaped instrument with a screw attached to it. The fine screw gauge can be difficult to use for rookies.

There are two scales used to measure the units:

1. Pitch scale
2. Circular scale

The pitch scale is the primary scale and can be seen as a vertical line attached to the instrument. It measures the units in millimetres per revolution. A circular scale is placed horizontally. Half of the millimetre is the circular scale in displacement called a micrometre screw gauge.

Screw gauge uses two formulas to calculate the outcome. Either pitch of the screw gauge or least count of screw gauge is used. The third formula is the calculation of the least count of the micrometre and has limited useability.

Pitch of the screw gauge – The pitch of the screw gauge is the ratio between distance moved by a screw and the number of rotations. The formula of the pitch is illustrated below:

• Pitch of the screw gauge = (moving distance by a screw)/ (number of rotations).

Least count of the screw gauge – The least count of the screw gauge can be calculated by the ratio of pitch and the total number of divisions. The formula of least count of screw gauge is as follows:

• Least count of screw gauge = (Pitch)/(number of divisions)
• Least count of micrometer screw gauge = (1 mm)/(100) = 0.01 mm

A micrometre screw gauge can be used to calculate the diameter of a small metal object in millimetres, such as sheets and glass. The formula for the same is shown below:

• Least count of micrometer = (pitch) / total number of divisions

1. Some parts of the screw gauge are movable, such as the anvil, sleeve, thimble, ratchet stop, spindle, etc.
2. The first step is to clean the spindle and anvil and place the clean cloth between the spindle and anvil. It is preferred to do it to get accurate results.
3. After cleaning, the next step is to place the object between the spindle and anvil.
4. To tight the instrument, rotate it in a clockwise direction.
5. Lock the thimble and then take the object out after some time.
6. Before doing so, write down the reading of the measurement.

Screw Gauge in Class 11

The chapter ‘Units and Measurements’ hold a weightage of seven marks, consisting of two short questions (one mark each) and two shorts questions (two marks and three marks simultaneously).

1) Explain the formula used to calculate the least count of the screw gauge.

Answer: Least count of screw gauge = (Pitch)/(number of divisions).

2) Write down the formula to calculate the least count of a micrometre.

Answer: Least count of micrometre = (pitch)/total number of divisions.

3) Explain the term ‘Precision Instruments.’

Answer: Precision instruments are the devices that can measure the minimum fraction of mm, e.g., Vernier Callipers and Screw Gauge.

Q: What is the function of a screw gauge?

Q: What do you understand by the pitch of a screw gauge?

Q: Which two units are used to measure the pitch?

Q: What is the formula to calculate the pitch of the screw gauge?

Q: What are the two essential parts of a screw gauge?