Now That's Fitting
A fitting (or connector) is the general category of hardware that connects hoses. Under that fall several different kinds of hose clamps and hose ends. First, let's talk clamps. A hose clamp is used to secure rubber or low-pressure braided steel over a fitting. For example, you attach rubber line to a carburetor by running the hose over the carb end and securing it with a hose clamp.
There are two main clamp styles: screw and spring. Screw-style clamps (or worm gear) simply wrap around the hose and then you tighten it. It's the standard ol' everyday stainless steel clamp. A spring type is a steel ring. You grab the end of the spring with pliers to open it, then slide it over the hose and it clamps automatically.
At the opposite end is the extended wing nut clamp, which is specialized and used in racing applications. It features a screw that's longer than a worm gear's, which allows you to tighten it by hand. There's also an Adel clamp, which is also called a nylon or cushion clamp. It has an aluminum band with a rubber insert that helps protect it from vibration. This clamp is used to secure lines along the framerails rather than to connect hoses.
We mentioned that a hose clamp can be used to secure a low-pressure braided line; however, the preferred way to make the connection is with a hose end for braided line and with an inverted flare for hard line. Hose ends come in straight, 30-, 45-, 60-, 90-, 120-, 150-, and 180- degree angles. It's comprised of a socket, a nipple, a cutter, and a swivel nut. Inside each swivel nut is a female AN thread (a male hose end is very rare) that connects the hose to a fluid source. Threads come in SAE, metric, AN, and pipe, and are male or female; male threads run on the outside of the adapter, female on the inside.
Now let's say you're connecting the transmission to the cooler and the threads on the hose end and the cooler are male and female. Well, that's a simple connection. However, if the hose end and the cooler both have female fittings, you need an adapter. An adapter converts the threads, and comes in straight, 45- and 90-degree configurations.
Often a factory hard line will run the length of the frame, then rubber line is used to connect to the fuel pump. The connection from hard to rubber can be made with a hose clamp because the flare at the end of the hard line will prevent the rubber from slipping off, and the clamp will seal it.
If the fuel pump has female pipe threads you need a pipe nipple fitting that's the same size as the rubber hose, which is usually 5/16 or 3/8 inch, in order to make the connection of the rubber line to the pump. Then you need an adapter with male pipe and a hex, which creates a barb similar to the flare at the end of a hard line. You'll need adapters for both the inlet and outlet sides of the pump. However, if you're connecting braided steel to the carb, you need an adapter with a hex for tightening.
These are adapters from Earl's. The one on the left is a 90-degree fitting. It's drilled aluminum block and is hollow inside. The other is a tube type, which is bent tube rather than drilled. Since it's a continuous tube, flow is smoother; the 90-degree's sharp angle is designed for easy threading if you're trying to make a connection where something like the frame is in the way. These are male threads since they're on the outside of the adapter. | 
This hose separator is from Earl's. This is important to have if you're running parallel braided-steel lines. Instead of using tie-wrap, which can abrade the hoses, many people plumb the hoses through a separator. | 
Here's a worm gear (top) and a cushion clamp. The worm gear is a common hose clamp. The cushion clamp gets its name from the cushion around it which reduces vibration. |
Make sure you run a hose with plenty of flexibility. It needs to have nice, smooth bends, and if it seems to be tugging, as shown in the bottom photo, the line isn't long enough. | 
A few sealant tips: Use Teflon tape only on a pipe fitting--since the threads seal by crushing, it's quite effective. However, using sealant will distort the threads. Don't use Teflon tape on an AN swivel because the tape will ruin the metal-to-metal connection. Tape is OK for coolant lines, but not for fuel or oil. | 
A banjo fitting, such as this one from Earl's, is used only for brake lines and is usually found on GM calipers. It gets its name from the loop on the end, which makes the fitting resemble a banjo. How does it work? Basically, fluid flows through a hole in the loop and a hole drilled into the bolt that goes into the loop. Then the bolt threads into the caliper. |