What wall thickness must copper tube have according to the specified standards?

The correct answer is based on the accepted standards for copper tubing used in sprinkler systems. Copper tubing is classified into different types—Type K, Type L, and Type M—each with varying wall thicknesses to accommodate different applications.

Type K copper tubing has the thickest walls, providing higher pressure ratings and durability, making it suitable for underground applications. Type L has medium wall thickness, often used for general plumbing and heating purposes, while Type M has the thinnest walls among these types, typically used in low-pressure applications.

In the context of sprinkler systems, the requirement for specific wall thickness contributes to the reliability of the system under pressure and the longevity of the materials used. Standards typically dictate the use of Type K, L, or M depending on the specific application and environmental conditions.

The other options do not meet the specifications for standard applications in sprinkler fitting, either by lacking the proper classification or by indicating no specific requirement, which doesn't align with the need for reliable and certified materials in this field. Thus, the classification of wall thickness as Type K, L, or M is essential for ensuring appropriate performance and compliance with industry standards.