Caliper

What is a caliper?

The caliper is an instrument used to accurately measure the dimensions of small objects. It consists of a graduated ruler with a fixed jaw, over which a slider moves. The caliper has two measuring jaws: one attached to the scale and the other to the slider.

What is a caliper used for?

With a caliper, we can measure various objects, such as screws, nuts, pipes, among others. To take a measurement, simply place the object between the jaws and slide the cursor until the piece fits snugly.

Who invented the caliper and how are its measurements taken?

The caliper usually has graduations in centimeters and inches. The sliding cursor has a measuring scale called a vernier. This scale is called vernier in honor of its creators: the Portuguese Pedro Nunes and the French Pierre Vernier. The vernier has a scale with *n* divisions corresponding to *X* mm of the fixed scale.

In the example beside, the vernier is divided into 10 equal parts corresponding to 9 mm. That means the first mark of the vernier is 1/10 mm before the fixed scale mark, the second is 2/10 mm before, and so on.

Parts of the caliper

A caliper consists of:

1. Fixed jaw
2. Movable jaw
3. Vernier scale (inches)
4. Screw and lock
5. Slider
6. Main scale
7. Fixed nib
8. Fixed stop
9. Movable stop
10. Movable nib
11. Vernier scale (millimeters)
12. Thumb wheel
13. Main millimeter scale
14. Depth rod

Types of calipers

There are several types of calipers available on the market. Below are the main instruments, their respective features, and a representative image.

Universal caliper	The most commonly used caliper. Suitable for internal, external, depth, and step measurements.
Universal caliper with dial	Has a dial attached to the slider that facilitates reading, making measurement faster.
Caliper with movable jaw (tilting)	Mainly used to measure conical parts or recessed parts with different diameters.
Depth caliper	Used to measure the depth of blind holes, grooves, recesses, among others. It may have a simple or hooked rod.
Gear tooth caliper	Used to measure gear teeth.
Digital caliper	Allows fast reading, free from parallax error, and is ideal for statistical control.

Example of caliper usage

In the animation above, you can see how a caliper works and how the measurement is performed. This is the way a caliper reading is taken.

How to use a caliper

To be used correctly, the caliper must:

• Have its slider and jaws clean, and the piece must be properly positioned between the jaws;
• Not be exposed to direct sunlight;
• Not be disassembled;
• Be protected from shocks or sudden movements;
• Avoid excessive tightening of the jaws against the object being measured.

See the videos below for the correct use of the caliper: