How to Install AN Hose Ends: Rubber-Lined and PTFE Braided Hose

A step-by-step guide to building leak-free AN lines with rubber-lined and PTFE braided hose

Building your own AN lines is one of the most satisfying parts of plumbing a car, and it is not difficult with the right tools and a little patience. Most leaks trace back to one of three things: a ragged cut, a hose that was not fully seated, or a fitting that was over-tightened. This guide walks through each step so you can avoid all three.

Need help with sizing first? See our AN Fitting & Hose Size Chart for dash sizes, threads, and how to pick the right hose type.

Before You Start: Match the Hose End to the Hose

Rubber-lined braided hose and PTFE-lined hose use different hose ends, and they are not interchangeable.

• Rubber-lined hose (stainless or nylon braided) uses standard hose ends, where the socket threads onto the hose and the nipple threads into the liner.
• PTFE-lined hose uses PTFE hose ends with a compression olive that seals against the PTFE liner. Our PTFE hose is designed for use with our PTFE hose ends.

Tools You Will Need

• Bench vise with soft aluminum or plastic jaws
• Masking tape or electrical tape
• Fine-tooth hacksaw (32 teeth per inch), hose cutting shears, or an abrasive cut-off saw
• Side cutters or flush cutters for trimming stray braid
• AN wrenches or properly sized open-end wrenches (not an adjustable wrench)
• Assembly lube: 30-weight motor oil or anti-seize
• Paint pen or marker
• For PTFE hose: a braid spreader or small pick
• Compressed air and a solvent for cleaning

Step 1: Measure and Mark the Hose

Route the hose on the car first, following the path it will actually take, and keep it away from exhaust, sharp edges, and moving parts. Leave a little slack for engine movement and avoid tight bends right at the hose end.

For a precise length, measure center-to-center between the two ports, then subtract the length each hose end adds. That added length is different for straight, 45°, and 90° ends, so measure your hose ends or check their dimensions before you cut.

Step 2: Make a Clean, Square Cut

1. Wrap tape tightly around the hose at your mark. The tape holds the braid together while you cut.
2. Clamp the hose lightly in the vise. Too much pressure will flatten it.
3. Cut straight through the center of the tape, keeping the cut square to the hose. Hose shears or a fine-tooth hacksaw give the cleanest result. An abrasive cut-off wheel works but leaves debris that must be cleaned out. Avoid cable cutters and chisels, which crush the liner.
4. Remove the tape and trim any loose braid strands flush with side cutters.
5. If the liner was squeezed out of round, gently reshape it with a pick so it will slide over the nipple.

Step 3A: Assemble Rubber-Lined Hose Ends

1. Clamp the socket (the outer threaded piece) in the vise using soft jaws. Never clamp on anodized surfaces with bare steel jaws.
2. Thread the hose into the socket by pushing and turning it counter-clockwise until it bottoms out against the bottom of the socket threads.
3. Mark the hose at the edge of the socket with a paint pen. This line will show you if the hose pushes out during assembly.
4. Lube the nipple threads and the inside of the hose liner with 30-weight oil or anti-seize.
5. Start the nipple by hand, threading it clockwise into the socket and liner.
6. Tighten with an AN wrench until the gap between the nipple hex and the socket is roughly 0.060"–0.080", about the thickness of a couple of credit cards. The hex does not need to bottom out.
7. Check your mark. If the hose has pushed back more than about 1/16" from the socket, take it apart and start over with a fresh cut.

Step 3B: Assemble PTFE Hose Ends

1. Slide the socket onto the hose, threaded end facing the cut, and push it down the hose out of the way.
2. Spread the braid slightly at the cut end with a braid spreader or pick so the olive can slip between the braid and the PTFE liner.
3. Install the olive over the PTFE liner, under the braid, and push it on until the liner seats fully against the olive's inner shoulder. No braid strands should be trapped between the olive and the liner.
4. Lube the threads of the nipple and socket.
5. Insert the nipple into the liner, slide the socket up, and thread the two together by hand.
6. Tighten with an AN wrench until the socket is snug against the nipple. The olive compresses the liner as you tighten, so do not exceed the snug point.

Step 4: Clean and Test the Assembly

1. Flush the inside of the hose with solvent and blow it out with compressed air to remove any cutting debris.
2. Pressure test before installing. A common method is to cap one end, apply low air pressure, and submerge the assembly in water. Bubbles mean a leak.
3. Cap or tape the ends until installation to keep dirt out.

Step 5: Install the Line

• Put a drop of oil on the B-nut threads and the flare. Do not use thread tape or sealant on AN flares. The 37° flare is the seal.
• Thread the B-nut on by hand until it seats. If it binds, stop and check for a mismatched thread or flare.
• Snug it with an AN wrench. Aluminum fittings only need moderate torque; over-tightening distorts the flare and causes leaks rather than fixing them.

Tightening Guide for Aluminum AN Fittings

Industry-typical values with lubricated threads. Start at the low end of the range. AN wrenches don't fit most torque wrenches, so if you are tightening by feel: snug the fitting by hand until it seats, then turn it a small amount more with a wrench, roughly a quarter turn. Stop there and leak check.

Troubleshooting Leaks

• Leak at the hose end socket: Usually a crooked cut, a hose that was not fully seated, or loose braid caught in the assembly. Recut and reassemble.
• Leak at the B-nut: Check for a damaged or dirty flare, a 45° fitting mixed with a 37° fitting, or sealant on the flare. Tightening harder rarely fixes it.
• Leak at an NPT adapter: NPT threads need sealant. Clean and reseal the pipe threads.
• Leak at an ORB adapter: Check that the O-ring is present, undamaged, and lubed, and that it was not pinched on installation.

Shop AN Fittings and Hose

We carry AN fittings, hose ends, adapters, and flexible race hose in stainless braided, nylon braided, and PTFE-lined versions. If you have a question about your setup, email us at sales@aceraceparts.com.