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Screw Gauge - Definition, Formula, FAQs

Screw Gauge - Definition, Formula, FAQs

Team Careers360Updated on 02 Jul 2025, 04:35 PM IST

What is a Screw gauge?

A screw gauge is a tool that usually makes it easy to measure the width or radius or the thickness of a thin wire or even the thickness of a thin metal wire with great accuracy.
This tool consists mainly of a U-shaped frame and a nail (or screw) attached to a thimble. There are usually two scales known as the Pitch of screw gauge Scale which is a large scale and is written on a barrel with vertical lines. The other is a circular circle inscribed horizontally on the thigh. Pitch of screw gauge scale measures the distance in millimeters (mm) propelled by a spindle for each change. Another change in a circular motion equal to half a millimeter of screw transfer is called a micrometer screw gauge. Micrometer scales are very accurate and accurate compared to the Vernier Caliper scale.

Before you start measuring, it is important to make sure that the 'Stud-end' and 'Spindle (or Screw) end' areas are cleaned; otherwise the measurements obtained will provide the wrong size.

‘Anvil’ is motionless and attached to the U-shaped frame. When the anvil and the spinning tin (or screw) are touched, the Pitch of the screw gauge Scale zero (or large zero scale) must correspond to the zero of the circular scale. This is considered a reference.

screw gauge

As the anvil is repaired, therefore, it is appropriate to place the object, its size to be measured, firmly near the temple. At the same time, a circular thimble at one end of the gauge needs clockwise rotation. This action will cause the spinning section (or screw) to move forward in the direction of the anvil. Continue to rotate the scepter so that the spindle (or screw) reaches the object, which is placed near the temple.

In the latter case, the object, the size of which is available, must be held firmly and firmly between the temple and the tile. A three-click Ratchet is used as long as a direct spinning operation is performed. This position can be locked using the lock key located next to the spinning wheel.

Once the previous step is detected, the pitch of screw gauge scale and the circular scale should be read. The pitch of screw gauge scale reading is the significance of the Pitch of screw gauge scale when it touches the sleeve of a circular scale. Round scale reading is a line-based reading on a pitch of screw gauge scale. A magnifying glass can be used to read measurements. Suppose a reading of a field is 'X' and a circular reading is a 'Y'.

The final calculation will be as follows:

Total reading = X (mm) + (Y x LC gauge) mm

Here, LC is a very small number of gauges.

Also read -

Screw gauge measurement using Inch Micrometer. Define gauge.

The value of the pitch of screw gauge scale is calculated in half an inch. The number 5 (or graduation 5) in the barrel means half an inch or 0.500 inches. There are 4 stages between graduation 0 and graduation 1 on the pitch of screw gauge scale. Therefore, the first graduation seen in the bin as number 1 is actually the 10th inch or 0.100 inches or 100th of 1000 inches. Similarly, 2 graduates are 0.200 inches or 200th of 1000 inches or 20 200 inches. So the smallest separation on the pitch of screw gauge scale can be 0.025 inches or 25th of 1000 inches.

Screw gauge formula: micrometer least count formula

Pitch of screw gauge scale measures the distance in millimeters (mm) that the spindle moves by each turn. The volume of the screw pitch gauge scale is calculated as given below:

Pitch of screw gauge of the Screw gauge = The distance traveled by the screw Rotation value

To measure the size of a small wire or a small sheet using a screw gauge, one needs to know a small calculation. The minimum screw pitch gauge calculation can be calculated using the formula given below:

Small screw gauge calculation = Screw Number Pitch of screw gauge for circular scale sections

Once the minimum number of gauges has been calculated, the final reading is calculated as below

Related Topics,

Complete Reading = High-Level Reading + Circular Circle reading x LC gauge.

The LC in the above equation is a small gauge calculation. There may be a chance that the zero of the pitch of screw gauge scale does not correspond to the zero of the circular scale. In that case, either the scale can be above or below the pitch of screw gauge scale (also known as the larger scale).

If the zero of the circular scale is less than the pitch of the screw gauge scale, it is known as the correct zero error. The value of the circular separation below the pitch of screw gauge scale should be multiplied by a small gauge count. This value should be deducted from the full study of the appropriate values. So the formula is as follows:

Complete Reading = Circular Scale Reading

If the zero of the circular scale exceeds the pitch of the screw gauge scale, it is known as a non-zero error. The value of the circular separation above the pitch of screw gauge scale should be multiplied by a small gauge count. This number will be included in the full study of the relevant estimates. So the formula is as follows:

Complete Reading = Circular Scale Reading

An example of how to read a screw gauge measure using a micrometer is discussed.

If a micrometer has a pitch of screw gauge of 0.5 mm. It means that with one complete rotation of the thimble scale, a distance of 0.5 mm travels through the thread. There are 50 sections on a circular scale. The minimum calculation will be 0.01 mm calculated as below.

Minimum number = Pitch of screw gauge Number = 0.550 = 0.01mm

Hence the pitch of screw gauge scale reading is 3 mm. According to a circular scale reading, 46 divisions are like a reference line on a pitch of screw gauge scale. So the full reading will be

Complete Reading = High-Level Reading + Circular Circle reading x LC gauge

= 3mm + 46 × 0.01 mm = 3.46 mm.

Also, check-

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NCERT Physics Notes:

Commonly Asked Questions

Q: How does the principle of a screw gauge work?
A:
The screw gauge works on the principle of a screw thread. As the screw is rotated, it advances or retreats by a fixed distance for each complete turn. This fixed distance is called the pitch of the screw. By counting the number of rotations and fractions of rotations, very small distances can be measured accurately. The main scale (sleeve) shows whole millimeters, while the circular scale (thimble) allows for reading fractions of a millimeter, typically to 0.01 mm precision.
Q: What is the least count of a typical screw gauge?
A:
The least count of a typical screw gauge is 0.01 mm (or 10 micrometers). This means it can measure dimensions to the nearest hundredth of a millimeter. The least count is determined by the pitch of the screw (usually 0.5 mm) divided by the number of divisions on the circular scale (usually 50). Some high-precision screw gauges may have a least count of 0.001 mm.
Q: How does the pitch of a screw gauge affect its measurements?
A:
The pitch of a screw gauge is the distance the spindle moves for one complete rotation of the thimble. It directly affects the precision of measurements. A smaller pitch allows for finer measurements. Most screw gauges have a pitch of 0.5 mm, meaning the spindle advances 0.5 mm for each complete rotation. The pitch, combined with the number of divisions on the thimble, determines the least count of the instrument.
Q: How do you read a screw gauge?
A:
To read a screw gauge:
Q: What is zero error in a screw gauge and how does it affect measurements?
A:
Zero error in a screw gauge is the deviation from zero when the spindle is in contact with the anvil. It can be positive (if the zero on the thimble scale is above the reference line) or negative (if it's below). Zero error affects all measurements and must be accounted for by adding it to (for negative error) or subtracting it from (for positive error) each reading to get the true value. Regular calibration helps minimize zero error.

Frequently Asked Questions (FAQs)

Q: How does the concept of mechanical advantage apply to a screw gauge?
A:
The concept of mechanical advantage in a screw gauge relates to how a small rotation of the thimble translates into a very small linear movement of the spindle:
Q: What are the limitations of a screw gauge in measuring very thin objects?
A:
While screw gauges are precise instruments, they have limitations when measuring very thin objects:
Q: How does the circular scale on the thimble of a screw gauge enhance measurement precision?
A:
The circular scale on the thimble of a screw gauge significantly enhances measurement precision:
Q: What role does friction play in screw gauge measurements, and how is it managed?
A:
Friction plays a crucial role in screw gauge measurements:
Q: How does the screw gauge compare to other precision measuring instruments like vernier calipers?
A:
Screw gauges and vernier calipers are both precision measuring instruments, but they have distinct characteristics:
Q: How does the principle of vernier scale apply to a screw gauge?
A:
While a screw gauge doesn't use a vernier scale directly, it applies a similar principle of subdividing measurements for greater precision. In a screw gauge:
Q: What is the relationship between the pitch of the screw and the number of divisions on the thimble?
A:
The relationship between the pitch of the screw and the number of divisions on the thimble determines the least count of the screw gauge. The formula is:
Q: How does wear and tear affect the accuracy of a screw gauge over time?
A:
Wear and tear can significantly affect the accuracy of a screw gauge over time:
Q: Can a screw gauge be used to measure internal diameters?
A:
Standard screw gauges are designed to measure external dimensions and are not suitable for measuring internal diameters. However, there are specialized versions called internal micrometers or bore gauges that can measure internal diameters. These tools work on similar principles but have a different configuration to access internal spaces. For precise internal measurements, it's important to use the appropriate tool rather than trying to adapt a standard external screw gauge.
Q: What are the main parts of a screw gauge?
A:
The main parts of a screw gauge include:
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