Are Type K, L, and M tubes sized based on the actual outside diameter measurement?

The correct answer is based on the understanding that Type K, L, and M copper tubes are not sized according to their actual outside diameter measurements. Instead, these tubes are classified by nominal size, which means the size designations (like 1/2 inch, 3/4 inch, etc.) correspond to standard dimensions established by industry standards.

In the copper tube industry, the actual outside diameter (OD) and wall thickness vary depending on the type of tube. For example, Type K has the thickest walls, followed by Type L, and Type M has the thinnest walls. Though they all have specific outside diameters that are standardized, the nominal sizing convention does not correspond to their actual measurements. This can lead to somewhat misleading assumptions if one expects the sizing to reflect actual dimensions.

Understanding this distinction is crucial for proper selection and applications of piping systems, particularly in plumbing and heating installations. Knowing that these tubes come in a variety of wall thicknesses with the same nominal size allows professionals to choose the right type for specific pressures and applications while adhering to local codes and standards.