What device is typically used to attach a blow line to pass it through a duct?

The correct choice is a bird. In the context of ductwork and blow lines, a "bird" is commonly referred to as a “fish tape” or “duct rod,” which is a tool used to route wire or cables through conduits and ducts. When attaching a blow line, the bird helps guide the line through the duct effectively and can navigate bends or turns within the duct system.

Using a bird is advantageous because it allows for smooth passage without getting stuck, facilitating the pulling of materials through confined spaces. This tool is designed for this purpose, making it the most suitable option in this scenario.

The other options, while they may serve a purpose in various applications, do not specifically address the need for attaching and guiding a blow line through a duct in the same effective manner as the bird does.