There are several systems on an SL-C (or any race car) that use hydraulic fittings and hose. For example, brake lines, fuel lines, oil lines, the lift kit lines, etc, all use hydraulic fittings and hoses to move fluid. It's vital to get these right, as they typically carry the lifeblood of an engine or other key parts. Sometimes the nomenclature and array of choices is daunting for new builders- but it doesn't have to be that way. This page is a brief primer on hydraulic fittings and hose as it relates to the SL-C.
The topic is way too broad to cover in a single page, but there are several good sources of more detailed information, starting with the bible of plumbing for motorsports, Carroll Smith's Nuts, Bolts, Fastener and Plumbing Handbook. More detailed info about these standards is available on Wikipedia, and elsewhere on the internet.
Unfortunately, there is no one standard that applies universally to all fittings and hoses. But you already guessed that, right? :) However, the standards that concern us for plumbing a car like the SL-C are pretty simple, and not too difficult to understand.
This standard came about during WW2, in an attempt to harmonize different standards in the US armed services, notably the Navy and Army. In fact, the "AN" name refers to A(rmy) and N(avy). So how does that relate to the SL-C? After the war, when the motorsports community really began to take off, there was a tremendous amount of war surplus material around, and as usual, hot rodders made use of these high-quality fittings in automotive applications. They have since become the one of defacto standards for motorsports plumbing.
Wikipedia has a great section on AN fittings here for more details.
As the supply of surplus AN fittings began to dry up and the rest of the world needed new fittings for construction equipment, etc., the Joint Industry Council devised a very similar set of standards that were very close to AN fittings. Both AN and JIC fittings use a 37 degree flare, and very similar thread standard. The AN fittings use a slightly looser thread standard, and as a result, are much cheaper to manufacture. For our purposes, fittings and hose using the JIC standard are fundamentally equal to the more costly AN fittings.
These are really very different fittings than either AN or JIC, but are also used in the SL-C, so it's important to understand the differences. NPT fittings are coarse thread fittings that have a tapered thread, unlike a normal thread on a regular bolt. This means that the fitting becomes tighter as it is threaded in, even it there is nothing to be clamped, unlike a standard bolt thread.
These fittings, also known as "pipe threads" are used in places like the fuel tank, and radiator. It's important to understand where these are, and to use the appropriate fittings in the right places. One example: The fuel tank fittings for fuel drain and vent both have NPT-threaded bungs on the tank. You'll need to source adapter fittings from the NPT bungs on the tank to whatever you are using on the other end for hose- typically AN or JIC fittings.
It should be obvious that you can't mix NPT fittings with anything else.
Sometimes the normal range of fittings won't meet your needs. That's when specialty fittings come into play. One common specialty fitting is made by Jiffy Tite, which allows hoses to be quickly and safely disconnect without leaks. This is useful when you want to easily and quickly disconnect the engine from the chassis, as in a race car. A spare engine could be stored and replaced without even needing to add oil to the lines, or purge them.
All fittings in AN or JIC spec are measured in 1/16 inch increments. Thus, a -6 (pronounced "dash 6") fitting is 6/16" or 3/8" inside diameter. Likewise, a -16 hose would have an ID of 1 inch.
Wait- what about hoses?
Choosing the right hose is just as important as the fittings. In fact, the fittings and hoses should be chosen at the same time, as many fittings are only warranted to work with the same manufacturers hose line. This is another reason to choose one manufacturer's line.
It's also important to choose the right hose for the job. There are different kinds of hose, all targeted for a specific purpose. Some of the differences are the kind of covering (simple fabric, a stronger Kevlar cover, or stainless steel, for example), the pressure rating of the hose (don't use low-pressure hose for hydraulics, for example), and the material used in the hose (some are teflon lined to help retain fuel odors, some others are specifically designed to combat the exotic additives in modern fuels, etc).
Use the right hose for the purpose- don't just buy 20' of -6 hose thinking it's all the same for all applications
Nowadays, almost all motorsports plumbing is actually based on the JIC standard, even as they may be referred to casually as "AN". For our purposes, there is essentially no difference, and the fittings can actually be interchanged in almost all instances. True AN fittings are still available, but don't come in the wide range of colors and materials that are available in JIC, and of course, they cost much more, making them the choice only where they are still required (the military and some civilian aviation) or where a specific fitting is only available in AN.
Although all fittings for a standard are supposed to be identical, sometimes manufacturers make small "improvements" to minor things like the cutter, or other parts that can be proprietary while still meeting the standard. For that reason, it's best to choose one manufacturer and source all fittings on the car from them. This guarantees consistent fit, appearance and color across the entire car.