Final answer:
For installing resilient channels, 1-1/4" Type W fasteners are required to properly secure the channels to steel structures.
Step-by-step explanation:
When installing resilient channel, a 1-1/4" Type W fastener is required. This is because the 1-1/4" length is sufficient to secure the channel without causing damage to the structure it's being attached to, while Type W refers to the fine thread of the screw which is specifically designed for working with steel. Both the 1-1/4" size and the Type W thread are essential to ensure a secure and proper installation of resilient channels.