What piping component is known for supplying a vertical line for sprinkler lines?

The component that is specifically designed to supply a vertical line for sprinkler lines is the riser nipple. This component serves as an essential part of a fire sprinkler system, facilitating the connection of horizontal piping to vertical sprinkler lines.

The riser nipple is often a short length of pipe that connects the riser, which carries water vertically from a lower to upper level, to the horizontal distribution lines that branch out to the individual sprinkler heads. This vertical configuration is crucial in multi-story buildings, where sprinkler systems need to navigate between different floor levels effectively.

Although other components like the branch line and cross main have roles in distributing water to various parts of the system, they do not primarily serve the purpose of providing a vertical supply route. The term "sprinkler riser" could be confused with the riser nipple, but it typically refers to the entire assembly that includes the vertical pipe supplying water to the sprinkler system, rather than just the connecting fitting. Thus, the riser nipple is the most precise answer in this context.