Which tool is commonly used for measuring the internal diameter of pipes?

The caliper is commonly used for measuring the internal diameter of pipes because it is designed to provide accurate measurements and can easily fit inside pipes to gauge their internal dimensions. This tool features two jaws that can be adjusted to measure various sizes, making it particularly effective for getting precise readings on circular objects like pipes. Its versatility allows it to measure both external and internal dimensions, which is crucial when working with different pipe sizes in pipefitting tasks.

Measuring tapes are primarily used for longer lengths and external measurements, making them less suitable for the specific task of measuring internal diameters. Micrometers, while they can measure small internal dimensions with great precision, are not as practical for measuring the internal diameter of larger pipes or in situations where quick measurements are needed. Pipe wrenches are tools used for gripping and turning pipes, not for measuring dimensions. Thus, while the other tools have their uses, the caliper stands out as the best option for accurately measuring the internal diameter of pipes.