A flare nut wrench is used to loosen or tighten nuts on the ends of pipes. It is also called a tube wrench or line wrench.
The end of a flare wrench is not as open as a standard wrench but not fully enclosed like a box wrench. If a regular wrench can be described as U-shaped, a flare nut wrench is shaped like a C. The narrow opening is large enough to fit around the pipe the nut is attached to. Flare nut wrenches are often used in plumbing applications, where the extra thickness of the jaws helps prevent damage to the softer metals used to manufacture the nuts.