What is the primary purpose of a caliper?

A caliper is primarily designed to measure the dimensions of an object, specifically its outside and inside dimensions, as well as the depth of grooves or holes. The correct answer highlights that calipers can accurately capture the measurements of both external and internal curves, making them versatile tools in various fields, including automotive and woodworking.

While it is true that calipers can also be used to measure the depth of holes or the thickness of materials, their unique ability to handle curved surfaces is what sets them apart in precision measurement. This capability is especially important in applications requiring detailed and accurate dimensions, such as fitting parts together or inspecting manufactured components. Additionally, measuring threads per inch typically requires specialized tools like thread gauges rather than calipers, further emphasizing the appropriateness of the correct answer.