What units are used to measure very small lengths?

To measure very small lengths, we use units like millimeters (mm) and micrometers (μm). One millimeter is one-thousandth of a meter, and a micrometer is one-millionth of a meter. These units are useful for measuring small objects, like the thickness of a coin or the width of a hair. For example, the width of a pencil lead could be measured in millimeters, while the size of tiny cells or bacteria might be measured in micrometers.

This question related to Chapter 5 Science Curiosity Class 6th NCERT.
From the Chapter 5. Measurement of Length and Motion.
Give answer according to your understanding.