Which type of fasteners are explicitly excluded from being used if they protrude into the duct?

The type of fasteners that are explicitly excluded from being used if they protrude into the duct are screws. This is because screws can create obstructions within the ductwork that may interfere with airflow, cause noise, or lead to accumulation of debris, which can affect the efficiency and performance of the duct system. Additionally, any protruding fastener could potentially cause damage to the duct surfaces or the components within the duct, leading to potential leaks or other issues that compromise the duct's integrity.

In contrast, metal straps, plastic clips, and rivets do not have the same tendency to interfere with airflow or cause damage in the way that screws might if they protrude. The design and application of these fasteners allow for secure installation without intruding into the duct space, maintaining optimal airflow and system efficiency.