The standard practice for securing round metallic ducts involves the use of how many screws or rivets?

In standard practice for securing round metallic ducts, the use of three screws or rivets is recommended. This method provides adequate fastening strength to ensure that the ductwork remains securely connected, minimizing the risk of air leaks and maintaining efficient airflow.

Using three points of attachment helps distribute the load evenly and reduces the chances of any single point failing due to vibrations or changes in pressure, which can occur during system operation. This is particularly important in HVAC systems where efficiency and integrity are crucial for performance.

While fewer screws could be used, such as one or two, relying on those would not provide the same level of security and may lead to issues over time, such as increased noise or reduced energy efficiency due to air leaks. Four screws might offer an even more secure attachment, but three is the accepted and effective standard, providing balance between stability and labor efficiency.