AN Fitting Adapters Explained: ORB to AN and Flare Sizing
By DeatschWerks | Published: 2026-11-02
Category: How-to Guides
Learn how to match ORB to AN adapters, 4AN ORB to 6AN, and 4AN ORB to 5/16 hose barbs, plus how to install a male flare bulkhead fitting correctly.
Quick answer
Match the port thread to the adapter's ORB end and the hose or line to the opposite end, then tighten to the correct flare or ORB torque. Use the steps below to size, assemble, and leak-check each connection.
Why ORB and AN ends are not interchangeable
ORB (O-ring boss) ports seal with an O-ring against a machined boss, while AN flare fittings seal metal-to-metal at the cone. An ORB-to-AN adapter lets you connect the two systems without guessing which end goes where. The thread sizes may look similar, but the sealing method and required torque differ. Always confirm the port type before threading anything together.
When to step up or down in size
Adapters such as 4AN ORB to 6AN change the line size, which affects flow and pressure drop. Use them only when the downstream component or hose is genuinely a different size. Stepping up at a restrictive port can help, but stepping down can starve a pump or injector. If you are unsure, keep the adapter size matched to the hose end rather than adding a reducer.
Hose barb versus flare: choose by hose type
A 4AN ORB to 5/16 inch hose barb is for push-on or clamp-style rubber hose, not for AN braided line. A 4AN ORB to 6AN adapter is for a 6AN flare hose end. Mixing these up leads to leaks or a hose that will not seal. Check the hose construction first, then pick the adapter that matches it.
Step-by-step adapter sizing and installation
- Identify the port type and size: Clean the port and confirm whether it is ORB or AN flare. Measure the thread diameter or compare against a known fitting. For ORB, check the O-ring condition. Common mistake: assuming a 4AN ORB port is the same as a 4AN flare port. If the port has a flat boss and an O-ring groove, it is ORB.
- Match the adapter to the hose or line: Choose an adapter with the correct opposite end: hose barb for rubber hose, AN male for a flare hose end. For example, use a 4AN ORB to 5/16 inch barb for 5/16 inch rubber hose, or a 4AN ORB to 6AN adapter for a 6AN line. Checkpoint: the hose end must thread onto the adapter by hand. Never force a mismatched thread; it will leak or strip.
- Lubricate and tighten the ORB end: Apply a drop of clean oil to the O-ring. Thread the ORB end in by hand until it seats, then tighten to the manufacturer's torque spec. If no spec is available, snug it firmly without crushing the O-ring. Common mistake: over-tightening the ORB and damaging the O-ring or threads. The O-ring does the sealing; the threads only hold it in place.
- Assemble the flare or barb end: For a flare end, lubricate the cone and thread the hose end on by hand, then tighten to spec. For a barb, push the hose fully onto the barb and secure it with a clamp rated for the pressure. Checkpoint: the hose should not pull off the barb with moderate hand force. Use the correct clamp style for the hose material; fuel injection hose needs fuel-injection clamps.
- Install a bulkhead fitting through a panel: Drill the panel hole to the bulkhead thread size, insert the fitting, and tighten the supplied nut on the back side. Use a sealing washer if the panel is not flat. Common mistake: forgetting to de-burr the hole, which can cut the O-ring or washer. Support the panel while tightening to avoid distortion.
- Pressure-test and re-check: Pressurize the system with the intended fluid or air and check every joint for leaks. Wipe dry and inspect after 10 minutes. Re-torque if you see seepage. Checkpoint: a dry joint after the test is your pass; a weeping joint needs a new O-ring or re-seating. Always leak-test before driving; a drip under pressure can become a stream.
Product facts
- 4AN ORB to 5/16 in: 4AN ORB male to 5/16 inch hose barb, anodized DW Orange. Lets you connect a 4AN ORB port directly to a 5/16 inch rubber hose without an extra flare adapter.
4AN ORB to 5/16 in - 4AN ORB to 6AN Adapter: 4AN ORB male to 6AN male, anodized DW Orange. Steps a 4AN ORB port up to a 6AN line for higher flow or to match a 6AN hose end.
4AN ORB to 6AN Adapter - 10AN Male Flare Bulkhead Straight (with nut): 10AN male flare bulkhead straight, supplied with a nut. Provides a secure pass-through for a 10AN line through a panel or firewall, with the nut included for installation.
