What is the name of the structural member nailed between two rafters to provide support for long spans?

The structural member that is nailed between two rafters to provide additional support for long spans is called a collar tie. Collar ties are typically installed in the upper third of the roof and help to prevent the rafters from spreading apart under load, which is especially important in situations where the roof span is significant. This feature is crucial in maintaining the overall structural integrity of the roof, especially in areas subject to heavy snow loads or wind pressures.

In contrast, other terms like horse ties and bow ties might refer to different types of structural reinforcement or connectors but do not serve the same function as collar ties. Rafter jigs, on the other hand, typically refer to tools or devices used in the layout and cutting of rafters, rather than structural members that provide support.