When preparing a tube for a fitting, how clean should the end of the tube be?

The end of the tube should be clean for at least 1/4 of an inch to ensure proper fitting and joining when soldering or brazing. This cleanliness is crucial because any contaminants, such as grease, dirt, or oxidation on the surface can hinder the proper flow of solder or braze material and create weak joints. The specified 1/4 inch provides a sufficient area for the joint to be made effectively, allowing the solder to adhere properly to the surfaces being joined. This practice also helps to promote adequate heat transfer during the soldering or brazing process, which is essential for achieving a strong, leak-proof connection.

Having a clean surface engages better with the solder and enhances the integrity of the bond formed, preventing potential leaks or failures in the system. A completely spotless area might be ideal but is often impractical, while a roughly finished surface or an untouched area could leave impurities that affect the joint's quality. Thus, cleaning the specified length ensures the reliability and durability of the fitting.