What is generally true regarding the cleanliness of a tube before fitting?

The statement that the end of the tube should be clean for 1/4 of an inch is important because cleanliness is critical in soldering and brazing processes. Oxidation, dirt, or contaminants present on the surface of the tube can prevent proper adhesion of the solder or filler material, which can lead to weak joints and potential failure of the connection.

Cleaning the end of the tube ensures that sufficient surface area is free of oxides and contaminants, allowing for better penetration and bonding of the joining materials. In applications like plumbing or HVAC systems, where integrity and durability are paramount, ensuring a clean surface is a standard best practice.

Failing to maintain cleanliness, as suggested by other options, could create issues such as leaks or structural weak points in the connection. Therefore, ensuring a clean surface extending at least 1/4 of an inch from the end is a requirement for achieving a strong and reliable joint in soldering and brazing applications.