Pipe joined with grooved couplings must use a listed combination of what?

The correct answer is based on the requirement for compatibility and performance when using grooved couplings in piping systems. Grooved couplings are a popular option in sprinkler systems due to their ease of installation and ability to accommodate movement. However, to ensure safety and integrity of the piping system, it's essential to use a listed combination of couplings, gaskets, and groove dimensions that have been tested and approved for use together.

This combination ensures that the sealing mechanism provided by the gaskets is adequate, and that the groove dimensions are appropriate for the specific couplings being used. This is crucial because improper dimensions or incompatible components could lead to leaks or failures in the system. Using a listed combination guarantees that all parts will work harmoniously under operating conditions.

The other potential options focus on elements that don't directly pertain to the use of grooved couplings. Valves and fittings might be used in conjunction with a piping system but are not specific to the criteria set for grooved connections. Threads and sealants are applicable to different types of joints, and welds and clamps pertain to different methods of joining pipes altogether. Hence, the specific requirement for grooved piping ensures safety and functionality is maintained, making the selected answer the most relevant.