How can you identify the correct size of a pipe fitting?

Identifying the correct size of a pipe fitting is most effectively done by measuring the inner diameter of the fitting. This is because pipe fittings are designed primarily to fit over or inside pipes, and the inner diameter will determine whether it can accommodate the corresponding pipe size. The specifications for pipe fittings often reference the inner diameter to ensure a proper and snug fit onto the pipe.

The inner diameter is crucial, especially when considering factors such as flow rates and the fitting's compatibility with standard pipe sizes. Using this measurement helps to avoid leaks and ensures optimal performance in a plumbing system.

While other methods, such as checking the outer diameter or part number, can provide information, they may not always ensure compatibility with the specific needs of a plumbing project. Relying solely on the outer diameter may lead to mismatches since fittings are often designed to be inserted over a pipe, and the actual fitting size needed is fundamentally related to the pipe's inner diameter. The length of the fitting is less relevant when determining size, as fittings can vary in length without changing the diameter.