Fuel Line Instruction - Hold The LIne

Building AN Hoses And Flaring Hardlines Isn't Withcraft, It Just Takes The Right Tools And A Little Practice

Tony Huntimer Mar 3, 2009 0 Comment(s)
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Assembling braided lines and flaring hard lines isn’t black magic or something only mechanics can do. With the right tools, it’s a job that can be done by just about anyone. It’s also something that is often overlooked in auto-related magazine articles. We’ve seen tons of technical articles about running lines throughout a car, but rarely do we get instruction on the proper way to assemble hoses and flair lines. So with the help, and a little bit of tool-loaning, from the guys at Goodies Speed Shop in San Jose, California, we’re able to show you some tips that will help you through the process of bendin’, flarin’, and fittin’.

Camp 0904 25 Fuel Line Instruction Parts 2/24

8 Degrees of Separation

A common misconception is that you can flare a hardline with the same flaring tool used for your brake lines. Aircraft AN (Army-Navy) fittings seal with a 37- degree tapered seat, while brake lines and household appliances use a 45-degree tapered seat. The 8-degree difference isn’t much, and may seat temporarily in some cases, but the sealed surface area on the flare is very small when using the improper flare. It’s guaranteed to leak as soon as there are any vibrations present. It’s sure to cause the flare to slip, and the fluid that leaks out may catch fire. Make sure you are using a 37-degree flaring tool. There are a few different models, but the one used in this article is a ratcheting Ridgid flaring tool, model #377. It’s the best and easiest tool I’ve used for flaring. You simply align the yoke with the tube, tighten the handle until it starts to ratchet, and you’re done. I’ve seen online auctions for 37-degree flaring tools ranging from $30 to $120.


Nobody is a pro right off the bat, so you’re better off starting with a test project. Cut about 12-inches of hardline to practice with. The great thing about building a test piece is that you familiarize yourself with the flaring tool, tubing bender, and tubing cutter without damaging any fittings. The anodized tube nut and tube sleeve is completely reusable. Simply cut the tubing and remove the fittings from the test project. You could assemble the tubing without the tube nuts and sleeves during practice, but remember to install them before flaring the ends. Forgetting to put the ends on first can lead to many four letter words being thrown around the garage. Once you flare the end, the only fix is to cut the tubing shorter and start over.

The aluminum tubing used in this article is fuel line offered by Moroso. It’s thin-walled, seamless tubing and comes in 25-foot rolls of 3/8-inch, 1/2-inch, and 5/8-inch diameters. I’ve worked with cheaper off-brand aluminum tubing and had it split when flaring the end, so be careful. The Moroso fuel line is very easy to work with and can be easy to bend with your bare hands for gradual curves, but a tubing bender must be used when making more than a 15-degree bend. It’s also easy to kink your work and have to start over.

With a number of different types of benders on the market, it’s easier to find handheld, lever-type tubing benders for jobs using 1/2-inch or smaller tubing. When you get up into the 5/8-inch tubing you’ll find some less expensive coil spring tubing benders that actually work pretty good but don’t permit the tight radius you can get from the lever-type benders.

When building a system for your car, always bend all your hard lines before you put on the tube nuts and tube sleeves, then flare the ends. That way you don’t waste your time flaring if you accidentally kink your tubing. Another good idea is to run all your lines, but leave a few extra inches at each end and double check the length before flaring the ends. If you cut the line a little too short on a long run of tubing, cut a few inches off, flare the end, and build another short line and join them with a male flare union AN adapter fitting.

AN Hoses

Assembling AN hoses can be really difficult and can require lots of bandages. You’ve seen the bumper stickers that read, “Give Blood, Play Hockey.” They should sell bumper stickers that read, “Give Blood, Build AN Hoses.” The hardest part of building AN hoses is getting all the little stainless steel needles into the socket of the hose end. Those wires wreak havoc on fingertips during this process, but they don’t have to anymore. Koul Tools now has the tool that saves a lot of anguish and blood. It’s a basically a composite funnel that allows you to quickly jam the braided hose into the socket without the blood.

Follow the steps and you’ll see how easy building AN hoses and adapting them to aluminum or stainless hardlines can be.




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