What is a critical factor to check when measuring the gap between two pipes?

Center alignment is indeed a critical factor when measuring the gap between two pipes. This is because ensuring that the pipes are properly aligned at their centers is essential for achieving proper fit and function. Misalignment can lead to a variety of issues, including stress on the joints, leaks, and reduced efficiency in the system.

When the centers of the pipes are aligned, it helps maintain uniformity throughout the connected system, preventing strain that may arise from uneven connections. This alignment is particularly important in applications involving expansion and contraction due to temperature changes, where properly aligned pipes can better accommodate movement.

In contrast, while considerations such as surface finish, material thickness, and distance from the wall might have their own significance in piping installations, they do not directly influence the essential requirement of maintaining an optimal gap for alignment purposes. Therefore, focusing on center alignment is vital for ensuring the integrity of the piping system.