Hobbies Cars & Motorcycles What Is a Line Wrench? A Very Useful Mechanics Tool Share PINTEREST Email Print Use a line wrench on brake lines, gas lines, or adjustable cables. photo by Matt Wright, 2008 Cars & Motorcycles Cars Basics How Tos Reviews Classic Cars Corvettes Mustangs Tires & Wheels Motorcycles Used Cars Trucks ATVs & Off Road Public Transportation By Matthew Wright Matthew Wright Matthew Wright has been a freelance writer and editor for over 10 years and an automotive repair professional for three decades specializing in European vintage vehicles. Learn about our Editorial Process Updated on 03/22/17 If you are working with any type of fitting that is in-line - such as a brake line, fuel line, or any type of cable - a line wrench can be a life saver. Standard open end wrenches may not grip the hex well enough, which can lead to stripping - a real pain in the neck! To use a line wrench, just slip the open part of the wrench over the line, then slide it onto the hex part of the fitting.