AN Union Fittings, Couplers & Reducers

What Are AN Union Fittings?

An AN union fitting is a straight connector that joins two AN lines or hose ends into one sealed, serviceable joint you can take apart later. AN fittings trace back to a World War II Army-Navy specification that standardized thread and flare sizing across the military branches. Each one seals with a 37-degree flare instead of a gasket, so metal meets metal for a tight, reusable connection.

Unlike push-on or barbed connectors, a union threads together with a wrench and holds pressure in fuel, oil, coolant, and hydraulic systems. Because AN only mates with AN, you'll use unions and adapters to bridge sizes, thread types, or fixed ports, and you can browse General AN Fittings for adapters that fall outside the union category. New to the system? Start with our guide on how to assemble AN fittings and hose assemblies.

AN Union Fitting Sizes and How to Choose

AN union fittings are sized by a dash number, where each number equals 1/16 inch of nominal inside diameter. A -6 AN union, for example, works out to 6/16 inch, or 3/8 inch. Match the union's dash size to the AN lines it connects, and use a reducer union when you need to step between two sizes.

• -3 AN and -4 AN: brake lines, clutch lines, and gauge or vacuum plumbing.
• -6 AN: carbureted and EFI fuel feed lines on most street builds.
• -8 AN and -10 AN: high-volume fuel systems, oil lines, and power steering.
• -12 AN to -20 AN: return lines, coolant, dry-sump, and large transmission cooler runs.

Check our AN fittings and hose sizes guide before you order so every thread and flare matches, and review fuel line size vs. pressure drop when you're sizing a fuel system.

Types of AN Unions, Couplers, and Reducers

AN unions come in several styles, and each one solves a different plumbing problem. The right choice comes down to whether you're joining matching lines, stepping between two sizes, passing through a panel, or mating ends that don't share the same gender.

• Straight unions: join two same-size AN lines into one continuous, in-line run.
• Reducer unions and union adapters: connect two different AN sizes, such as -8 AN to -6 AN.
• 90-degree and 45-degree unions: change direction in tight spaces without kinking the hose.
• Bulkhead unions: pass a line through a firewall, tank, or panel with a locking nut.
• Coupler fittings: mate two male or two female AN ends where the genders don't match.
• Push-lock union fittings: join push-on hose without wrenches or crimping tools.

Pair them with AN Hose & Hose Ends to complete a run, or seal off open ports and pass lines through panels with AN Bulkhead Fittings. Matching the union style to the job keeps your plumbing clean and leak-free.

Materials and Finishes for AN Union Fittings

Most AN union fittings are machined from lightweight 6061 aluminum and anodized to resist corrosion, while steel and stainless versions handle higher-abuse jobs. The anodizing does more than add color, since it hardens the surface and helps the fitting shrug off fuel, oil, and moisture. Anodized colors also let you coordinate a build or code your lines by function.

You'll find blue, red, and black anodized finishes, plus plain and Endura-style coatings that mimic stainless steel. Aluminum keeps weight down for street and race use, while zinc-plated and stainless steel add durability where fittings take repeated wrenching or see high heat. For fuel, oil, and coolant lines, aluminum is the common choice; for brake lines and corrosive environments, stainless earns its higher cost. Choose a finish that matches the rest of your AN Fittings & Hose for a clean, consistent look under the hood.

AN Union Fitting Brands at JEGS

JEGS stocks AN union fittings from the industry's top plumbing brands, so you can match a union to the hose ends and adapters you already run. Sticking with one brand across a system keeps thread quality, flare angle, and finish consistent from fitting to fitting. Earl's Performance Plumbing brought aviation fluid-transfer technology to performance cars and offers one of the widest union and reducer lineups.

Russell builds all-aluminum unions with a 37-degree sealing angle and a bright Endura finish, while Fragola Performance Systems offers aluminum couplers and reducer adapters across the full dash-size range. Vibrant Performance rounds out the selection with specialty adapters and connectors for custom and forced-induction builds. Each brand machines its unions to the same AN standard, so you can mix sizes and styles while keeping every joint sealed. Compare the brands above, then shop the AN union fittings selection now to finish your project in one order.