Subscribe to the Free

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
View Full Gallery

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.

1. The most important thing to know about adapting a hardline to aircraft style AN fittings is that AN fittings have a 37-degree flare seat. Your flaring tool for brake lines and household appliance lines flares tubing to 45 degrees. Here you can see the slight difference between the AN fitting (in the foreground) and a brass natural gas fitting (in the background). It doesn’t look like much of a difference, but the 8-degree difference is enough to produce a potentially dangerous leak, especially if you are working with fuel lines.

2. Build a small test project before actually bending your fuel lines. This will get you familiar with flaring and bending before wasting some valuable time and materials. Start off with about a 12-inch test piece. The best way to ensure a straight cut is to use a tubing cutter. Tighten the blade a little bit at a time and roll it around the tubing after each adjustment.

4.The aluminum tubing is extremely soft, so when you’re done cutting it the opening will be considerably smaller. Use a deburring tool to clean up the burr inside the end of the tubing.

5.There are a few different types of tubing benders on the market. This design is the easiest to use and can be found at most hardware stores.

6.This is a coil spring-type bender. It works good except it does not do as clean of a job as the lever-type bender and will not bend a very tight radius. It slides over the tubing and the coil helps keep the tubing from kinking.

7.Don’t forget to put the tube nut and sleeve on the tubing in the correct direction. Double-check them before flaring the end. If you get one backwards, you’re going to have a nice piece of scrap.

8.These instructions are for using a Ridgid Tools ratcheting flaring tool model number 377. Slip the tubing about 1/8-inch below the top surface of the flaring bar. If the tubing is too high, the flare will be too big for the tube nut to slip over. Slide the yoke over the center of the tubing to be flared. Turn the handle until it starts ratcheting and your flare is done.

9.Loosen the yoke and remove your flare from the flaring bar. Slide the tube sleeve and nut into place. If the tube nut doesn’t fit over the flare, your tubing was sticking up too far in the flaring bar. Cut it off and try again.

10.Now you’re ready to attach an AN fitting to your project. You can do so by using a male flare union (top) or you can assemble your braided hose with a hose end with a male flare (bottom).

11.You can also use a bulkhead male flare union to mount the line to a bracket or through a panel. Slip the union through the hole and thread on the nut for a rigid mount.

12.Here’s a cutaway view of an XRP fitting that shows all the features of their hose end, including exclusive patented features.  Unlike some competitors’ product, XRP fittings are hard anodized which prevents galling of the threads and helps protect the finish from tool marks and fading due to direct sunlight. (Illustration courtesy of XRP)

13.Wrap the hose with duct tape and cut the center of the tape. This helps reduce the amount of braid that frays during the process.

14. Expect a large amount of rubber debris left in the hose when you cut a hose with a hacksaw or a high-speed cutoff wheel. Depending on your application, this debris will go straight to your carburetor, engine bearings, or transmission. Using air to clean out the debris rarely does the job. Here I pulled a piece of paper towel through a hose with a wire.

15.Remove the tape before assembling the hose end. You’ll either never get the hose through the fitting or you’ll cause a serious leak if you leave on the tape.

16.Shoving the stainless braid into the socket end can be a bear if the braid has frayed too much. Those little wires will poke holes in your fingers in a hurry, so use a small screw driver or awl to coax the braid into the socket end.

17.Koul Tools has come out with a great new product that acts as a funnel to get all those steel finger pokers into the socket. It’s almost like a magic box for assembling braided hoses. XRP hose ends are smaller than others on the market, so Koul Tools ships a little disc to move the socket closer to the opening. I ended up wrapping a piece of tape around the socket to take up a little slack on the sides.

18.Clamp the Koul Tools composite tool into your vice. Confirm the socket is centered in the tool opening and wedge the end of the hose into the device. Turn the hose in a clockwise motion while pushing it into the tool. Within ten seconds the hose was all the way into the socket.

19.The hose end depth should be lined up with the insertion mark on the outside of the socket. The mark is just short of the depth of the threads inside of the socket. It’s also a tool used to determine the proper length to cut the hose for your application.

20.Tighten the nipple into the vice using aluminum vice jaws to safely hold it in place without damaging the finish. Put anti-seize lubricant on the threads and inside the hose to ease assembly. Be careful with anti-seize. It gets everywhere in a hurry.

21.Mark the hose end depth with tape or a permanent marker so you know if the hose pushes out during assembly. Tape can slip during assembly, so a permanent marker is a safer way to mark the hose.

22.Thread the hose and socket onto the nipple by hand as far as it will go to ensure you’re not cross-threading them. Be sure to push the hose with ample pressure while turning it to keep the hose from pushing out of the socket during assembly.

23.Use a wrench to finish tightening the assembly. If your wrench is damaged, there’s a good chance it will damage the anodized finish, so use a good one. You’re done tightening when there’s a gap of .030 or less between the socket and shoulder of the nipple.

24.By using the mark or tape on the hose, make sure the hose didn’t slip out of the socket during assembly. If it did slip, loosen the fitting and try again. If that doesn’t help, you may need to start over completely. For insurance, XRP suggests cleaning and then testing the hose at twice the maximum operating pressure. It should also be periodically checked for leaks under normal operating conditions.


Goodies Speed Shop
San Jose, CA 95126
Koul Tools
Lake Havasu City, AZ 86403
South Gate, CA 90280



Connect With Us

Get Latest News and Articles. Newsletter Sign Up

sponsored links

subscribe to the magazine

get digital get print