Choosing the Right AN Fitting for Fuel Rail Adapters
By DeatschWerks | Published: 2026-10-22
Category: Buying Guides
Learn how to select the correct AN fitting for your fuel rail adapter project, including ORB to AN couplers, NPT adapters, and Y blocks.
Quick answer
For a fuel rail adapter, start by matching the rail's port thread (usually ORB or NPT) to your AN line size, then choose a coupler or adapter that bridges the two without introducing extra leak points.
Understanding Fuel Rail Ports
Fuel rails commonly use O-Ring Boss (ORB) or National Pipe Taper (NPT) ports. ORB ports seal with an O-ring and require a straight thread adapter, while NPT ports seal on the tapered threads and need an NPT-to-AN adapter. Using the wrong type can cause leaks or damage the rail.
Thread Compatibility Matters
AN fittings use a 37-degree flare seal and are not directly compatible with NPT or ORB threads. You must use the correct transition fitting. For example, a 10AN ORB port needs a 10AN ORB to 6AN coupler to step down to a 6AN line. Skipping this adapter forces an improper seal.
Decision rules for fuel rail adapters
- Identify your rail port: Check if the fuel rail uses ORB (straight thread with O-ring) or NPT (tapered thread). ORB ports are common on aftermarket rails; NPT appears on some OEM-style rails.
- Match AN line size: Decide your fuel line size (e.g., 6AN, 8AN). Most street fuel systems use 6AN. For higher flow, step up to 8AN. The adapter must match both the rail port and your chosen AN size. If you need to split one 8AN line into two 6AN lines, use a Y block like the DeatschWerks 6AN x 2 to 8AN Y Block.
6AN x 2 to 8AN Y Block - Select the correct adapter: For ORB ports, use an ORB-to-AN coupler with the correct ORB size. For NPT ports, use an NPT-to-AN adapter. Ensure the adapter's AN side matches your line size. Always verify thread pitch and seal type before purchasing.
Product facts
- 10AN ORB to 6AN Coupler: DeatschWerks 10AN ORB to 6AN Coupler connects a 10AN ORB port to a 6AN male flare and includes an O-ring. This lets you adapt a common fuel rail ORB port directly to a 6AN line without extra fittings.
10AN ORB to 6AN Coupler - 6AN to 1/2 in NPT Adapter: DeatschWerks 6AN to 1/2 in NPT Adapter connects a 6AN male flare to a 1/2 inch male NPT thread in anodized matte black. Use this when your fuel rail has a 1/2 inch NPT port and you need to run a 6AN line.
Who should use this guide
Best for
- Builders adapting an aftermarket fuel rail with ORB ports to a 6AN fuel system
- Anyone replacing a fuel rail and needing to match existing AN lines
Not for
- Those using push-lock or barbed fittings on the fuel rail
- Applications requiring a direct AN-to-AN connection without thread adaptation
