Your truck's plumbing is made up of hoses (or lines) that help route fluids from one area to another. Every vehicle uses hoses, and such conditions as pressure, rate, and temperature vary for each specific application. Carbureted vehicles typically come stock with hard line from the gas tank to the engine, with only a few pieces of rubber. The heater, water, and vacuum lines are almost always rubber, while the brake system has extruded soft steel hard lines, with the exception of flexible hoses near suspension components.
Rubber and hard lines are measured by their inside diameter (id); fuel lines are available in ¼, 5/16, and 3/8 inches; heater lines are available in 5/8 and ¾ inches; and vacuum lines in ¼ and 11/32 inches. Radiator hose is the only one not sized by id, but rather by application.
Since rubber has a shelf life, it can flake when you cut it and can't always hold up to the type of fluid running through it. People often switch to hard or braided stainless steel hose. Braided steel refers to its outside covering, while the actual hose comes in either Teflon-lined or standard neoprene rubber. The inside is essentially the same as high-quality rubber hose, but the braided-steel exterior makes the hose highly resistant to abrasion. It can also raise the burst pressure in some applications. The Teflon version is usually used for the brakes, while the neoprene is utilized for fuel and so on. A braided-steel covering can also be put over your existing rubber hoses if you want to dress up your plumbing, but these coverings are for appearance only. Braided line is used for the fuel, water, heater, and external oil lines (commonly seen in racing and performance vehicles), and it can even be found in the brake system because the Teflon lining has a stiffness and won't give like rubber can. However, when it comes to your brakes, you must buy the line premade and not make it at home.
Braided lines are sized by a dash number determined by their id in 1/16 inch. For example, a 3/8-inch fuel line would be -6. This is Army Navy (AN) spec, a standard that began prior to World War I to organize hardware, and is the industry standard. Fuel lines come in -4 to -12; water and heater lines in -10 and -12; and radiator lines in -16 and -20.
Plumbing comes in rubber,...
Plumbing comes in rubber, braided-steel, and hard lines. The braided steel (top) has a braided stainless steel outer wrap and is flexible, while hard lines are stainless steel or steel tubing.
Here's an example of a neoprene-lined...
Here's an example of a neoprene-lined braided-steel hose and a convoluted Teflon-lined braided-steel hose. The convoluted or corrugated hose is lightweight and flexible so it's a popular hose. However, unlike the neoprene's smooth center, the convoluted hose features a spiral center that actually restricts flow.
The components of a hose end...
The components of a hose end are, from left to right, swivel nut, cutter, nipple, and socket. It has female AN thread to connect to an AN male fitting.