What are the key features and uses of a vernier caliper and a micrometer screw gauge, as depicted in the image?

The image describes two measuring instruments: the vernier caliper and the micrometer screw gauge.

• A vernier caliper is used to measure the thickness of objects, as well as their depth, internal, and external dimensions. Measurements are recorded using a main scale reading and a vernier scale reading to get the actual reading.

• A micrometer screw gauge offers better precision than a vernier caliper, with an accuracy of $0.001 \text{ cm}$. It is typically used to measure the diameters of small objects like wires and ball bearings. The diagram shows its main parts: the frame, anvil, spindle, sleeve (with the main scale), and thimble (with the rotating vernier scale division).