Custom CNC AN Fittings Guide: Types, Sizes, Materials, CNC Machining Cost & Surface Treatments

 

 

 

We know that AN hose end fittings are often used in automotive, racing modification, aerospace industry, and other high-pressure fluid delivery systems. AN stands for Army-Navy, because the specification is based on the flexible fluid connection standard used during World War II, so the AN standards ensure absolute reliability, precise sealing, and interchangeability under severe vibration, thermal expansion, and high pressure. AN fittings have a variety of different angles to assist wiring and gaps. They are straight, 30, 45, 60, 90, 120 , 150 or even 180 degrees.

 

And for designing custom fuel rails, oil cooling systems, dry-sump lubrication, or hydraulic lines, choosing the right AN hose end fittings combination (and understanding AN fitting CNC machining) is essential. This complete guide walks you through AN types, material options, surface finishing, quality control, and cost factors. At the end, we will also share you a case study of how we solved post-assembly sealing cone leaks of an-8 swivel hose fittings.

 

 

 

 

 

 

 

Types and Sizes of AN Fittings

 

 

 

 

Common types generally consist of crimping types, reusable hose ends, and push locks, and functional machined styles:

 

 

Crimp Type Connector:

 

It requires a hydraulic press with a specific mold to correctly crimp the collar to the end of the hose, so it is often used in facilities that manufacture a large number of hoses. These machines and molds are often expensive, so you won't see individuals or small fleets using them. Crimped hose requires a new crimp ring to be reused, but if crimped correctly, it is considered the strongest and most reliable joint.

 

 

Reusable Hose End:

 

The end of the hose uses a two-part system to hold the hose in place to be reusable. Practical performance is often used with braided hoses made of stainless steel or nylon braid.

 

 

 

AN Push Lock Hose End Fitting:

 

 

 

They are single-piece units with barbed ends, so push-lock hoses are the easiest to assemble. Push locks are used with coated hoses because they have no function to prevent the braid from spreading. The barb can be used alone to hold the hose in place, the hose is pressed against the barb and secured, or additional clamps can be used.

 

 

 

Functional Machined Fitting & Adapter Styles:

 

• AN Swivel Hose Ends: 360° rotating head allows independent orientation after tightening.
• PTFE Hose Ends: Uses brass/aluminum olive (ferrule) squeezed between socket & nipple.
• Y-Tee Block Splitters: Multi-port manifold block machined with minimal flow restriction.
• AN Male Flare Tees: T-shaped connector with 37° male AN flare seats on 2 or 3 ports.
• AN-to-NPT Adapters: Connects tapered pipe threads (NPT) to 37° male AN flare lines.
• AN Bulkhead Fittings: Extended threaded body locked with nut and washer.
• Male-to-Female Swivels: Position-adjustable adapters.
• AN-to-ORB Adapters: UNF straight threads with O-ring groove shoulder to 37° flare.
• Forged & CNC Hose Ends: Forged aluminum blank with CNC-finished threads and 37° cones.
• Reducers & Expanders: Step-down or step-up adapters (e.g., AN-10 Male to AN-8 Male).
• Quick-Connect Adapters: Push-to-connect OEM style adapters for female AN threads.

 

 

Size category:

 

Each size number has its own standard thread size, which has a specific relationship with the hose inner diameter, tube outer diameter, and SAE thread size. There are 13 types of AN fittings sizes from line 2 to line 32.

 

As shown below:

 

 

 

 

 

 

 

 

 

 

How are AN fittings made?

 

 

When the process or material is different in the manufacturing method, in order to let everyone better understand the aluminum parts as an example, the following shows you the production process.

 

1. The first step in the manufacturing process is to choose the right material (here we take 6061 aluminum as an example).
2. Prepare the production part of AN pipe fittings, including: pipe end, intermediate pipe, socket, nut and lock wire.
3. Making the middle tube: use the size reserved in the drawing to cut and bend the middle tube so that the middle tube can be obtained.
4. Pipe end parts: use CNC to make two identical pipe end aluminum parts.
5. Manufacture of sleeve and nut: Since this is a fixed part to prevent leakage, the material is selected for more durable alloy to make sleeve and nut.
6. Lock thread: Use metal cutting to prepare stainless steel thread.
7. Welding: Use welding technology to weld and polish the two pipes in the middle of the pipe until there are no omissions or welding traces.
8. Assembly: Assemble the manufactured parts and pipe fittings.

 

 

 

 

CNC AN Hose End Fittings: What Materials You Can Use?

 

 

 

 

CNC machining allows for various materials and high-precision manufacturing of AN fittings and hose components. Selecting the right material is critical, as it determines pressure tolerance, fluid compatibility, corrosion resistance, and overall weight in modern automotive, aerospace, motorsport, and marine applications.

 

 

 

 

 

 

oad Your AN Fitting Drawings

 

Surface Treatment Options for AN Fittings

 

 

 

 

Surface treatment services not only enhance the visual appearance of AN fittings but also provide critical protection against corrosion, wear, and chemical exposure in harsh environments. The most classic surface treatment options include:

 

 

A. Polishing: Mechanical buffing that creates a smooth, mirror-like or high-gloss finish,  reduces contaminant buildup and eases cleaning.

 

B. Bead Blasting: Blasting the AN fittings surface with glass or ceramic beads to achieve a uniform matte or satin finish. It hides minor machining marks, and creates a clean industrial appearance.

 

C. Single / Multi-Color Anodizing: An electrochemical process forming a durable protective oxide layer, available in classic red/blue, solid black, or custom multi-color finishes. It enhances surface hardness, prevents oxidation, and offers resistance to fuels, oils, and chemical exposure.

 

D. Powder Coating / Painting: Applying a cured powder or liquid paint layer in various solid or custom colors. It provides a thick, durable protective barrier against abrasion, impact, and aggressive environmental elements.

 

E. Screen Printing / Laser Marking: Applying logos, brand markings, or specification labels directly onto the surface using durable inks or laser etching. It provides permanent product identification and easy size verification during assembly or maintenance.

 

F. Precision Masking: Using high-temperature tape or custom plugs to protect critical threads and sealing seats from unwanted plating or anodizing during surface treatment.

 

G. Electroless Nickel Plating: An autocatalytic chemical process that deposits an even layer of nickel-phosphorus alloy over complex geometries, delivering exceptional corrosion resistance and thread wear protection.

 

H. Passivation: A chemical acid treatment for stainless steel fittings that removes surface iron impurities and enhances the natural protective oxide layer to prevent rust and chemical corrosion.

 

 

 

 

 

Cost Factors for CNC Machined Custom AN Fittings and Hose

 

 

 

Understanding the drivers of custom CNC AN fitting and hose costs helps you optimize designs for performance without exceeding project budgets.

 

• Raw Material Selection:

 

For example, aluminum 6061-T6 offers the most cost-effective solution. Titanium Grade 5 and 316L Stainless Steel significantly increase raw material costs and machining cycle times (due to lower cutting speeds and higher tool wear).

 

 

• CNC Machining Complexity & Tooling Axis: 

 

For instance, simple 3-axis CNC lathe turned fittings are the most economical. 45° and 90° elbow hose ends or Y-block splitters require multi-axis turn-mill centers or 5-axis CNC machining, increasing cycle time and fixture setup costs.

 

 

• Surface Treatment & Masking Labor: 

 

A common situation is like that: a single-color anodizing is cost effectively. But anodizing requiring hand-applied precision masking plugs for 37° flare cones adds specialized labor costs.

 

 

• Production Volume & Lot Sizes: 

 

High setup-to-run time ratio makes 1–10 piece prototypes more expensive per unit. Scaling to low-volume or production runs (100–1,000+ pieces) dramatically drops per-unit machining costs.

 

 

• Quality Control & Specialized Testing: 

 

100% thread gauge verification and dimensional inspection are standard. Adding specialized application-specific pressure testing (e.g., 3,000 PSI hydrostatic test) or CMM port position reporting increases inspection time and cost.

 

 

 

 

How to Check the Quality of AN Fittings?

 

 

 

 

Detection is a complex and precise process. Depending on your project requirements, quality inspection options include:

 

1. Application & Leakage Airtightness Test: AN fittings are designed for reliable, leak-proof fluid transfer. Hydrostatic pressure testing, pneumatic air-under-water bubble testing, or high-pressure helium leak detection are good pressure test ways to ensure assembled components maintain a flawless seal under operational loads.
2. Anti-Rust & Corrosion Test: Because AN fittings operate in harsh automotive, marine, or industrial environments, salt spray testing (NSS/AASS) is a reliable testing option to evaluate coating durability. Accelerated environmental exposure testing helps confirm long-term corrosion resistance and service life.
3. Surface Quality & Visual Inspection: Comprehensive visual and tactile quality checks verify that surface finishes (anodizing, plating, or polishing) are uniform and free of burrs, scratches, or color variations, preventing premature wear on sealing surfaces.
4. Dimensional & Thread Tolerance Check: Precise CNC machining relies on strict thread pitch and 37° flare geometry. Precision inspection using Go/No-Go thread gages, optical comparators, or CMM (Coordinate Measuring Machines) serves as a great solution to guarantee thread compatibility (UNF/UN/NPT/ORB) without binding or galling.
5. Material Composition & Hardness Test: XRF (X-ray Fluorescence) spectrographic analysis offers an effective way to confirm material grades (e.g., 6061-T6, 7075-T6 aluminum, or 316 stainless steel), while hardness testing serves as a practical option to verify torque resistance and pressure capabilities. And there are more other mechanical test ways to choose from if needed.

 

 

 

 

 

 

 

 

VMT CNC Machining Factory Case Study

 

 

 

 

Solving Post-Assembly Sealing Cone Leaks of AN-8 swivel hose fittings

 

 

A high-performance motorsport client approached us with persistent micro-leaking on custom 6061-T6 anodized AN-8 swivel hose fittings(made by their previous suppliers) installed on a 150 PSI oil cooler line. While all thread dimensions passed standard Go/No-Go thread gauge checks, fluid continued to weep past the 37° flare seat after 30 minutes of thermal cycling.

 

Our engineering team performed a detailed optical surface scan and coordinate inspection on the leaking units:

 

• Micro-Tool Marks on Flare Cone: The 37° male cone exhibited microscopic turning tool chatter marks (Ra 1.6 µm) running perpendicular to the seal path. Under thermal expansion, thin engine oil escaped along these micro-channels.
• Anodizing Layer Buildup Instability: Non-uniform decorative anodizing thickness on the unmasked 37° cone created micro-voids under tightening torque.
• Concentricity Runout: A 0.05 mm concentricity misalignment between the thread center axis and the 37° cone seat caused uneven seating pressure when torqued.

 

Then, we done the following ways to machine the AN-8 swivel hose fittings

 

• Single-Point Diamond Turning & Polishing: Re-programmed the CNC turning path using a single-point diamond finishing insert followed by automated micro-polishing, reducing surface roughness from Ra 1.6 µm down to Ra 0.4 µm.
• Precision Masking Implementation: Designed custom silicone cone caps to isolate the 37° flare seating surface during Type II anodizing, preserving pure, unetched metal-to-metal seating contact.
• Turn-Mill Single-Setup Machining: Combined thread turning and flare cone finishing into a single CNC lathe setup, reducing concentricity runout to < 0.008 mm.
• 100% Mating Cone Contact Inspection: Introduced an optical optical-comparator check and blue-layout seating contact test before shipping.

 

 

Results

 

 

The redesigned custom CNC AN-8 fittings achieved a 100% leak-free seal during hydrostatic testing up to 1,200 PSI, resolving the customer's field failure issues.

 

 

 

 

Summarize

 

 

When looking for AN fittings parts suppliers, it is sometimes difficult to determine the best fit for your needs. In order to help you choose the right factory, the following points must be met:

 

1. The factory must have a strong production capacity, including internal equipment such as CNC lathes, CNC milling machines, and bending machines.
2. The supplier should have a good procurement system and provide suitable materials to ensure quality.
3. The factory needs an excellent engineering team that can make AN Fittings according to the drawings and tolerances. If you need technical answers about the end of the hose, you can talk to an expert.
4. The company can do secondary processing and finishing for the safety accessories.
5. The factory should have a good quality control system and an experienced QC team. This can ensure the safety of your parts and funds.
6. The price may not be the cheapest, but it should be reasonable. In addition, the quotation turnover rate is fast and the delivery is fast.

 

VMT pursues the highest quality products and has passed ISO9001. We can guarantee our quality and service for any single project of our customers. VMT is an in-house manufacturing plant with advanced machines, including manufacturing machines, punching machines, CNC lathes, three-axis CNC machine tools, and high-precision five-axis CNC machine tools. This supports us in providing strong capabilities for any hose end fitting project. No matter how complex they are, Contact VMT to easily handle them. [2D Drawings (PDF files), 3D Drawings (IGS/STP/STEP files)].

 

 

 

 

FAQs

 

 

Q1: Can I use NPT fittings directly with AN fittings?

 

 

A: No, not directly. AN fittings seal on a 37° metal flare cone with straight UNF threads, whereas NPT fittings seal on tapered threads using thread sealant. To connect them, you must use a custom CNC-machined AN-to-NPT adapter.

 

 

 

Q2: What is the difference between AN 37° fittings and SAE 45° fittings?

 

 

A: AN fittings utilize a 37-degree flare angle and specific military UNF thread pitches. Standard automotive flare fittings (often found in plumbing or older domestic cars) use a 45-degree flare angle. Connecting a 37° AN fitting to a 45° SAE fitting will damage the seating surface and cause severe fluid leaks.

 

 

 

Q3: Why is my AN hose end leaking even though the fitting is tight?

 

 

A: Over-tightening an AN fitting can deform or crush the 37° aluminum seating cone, creating a permanent leak path. Other common causes include burrs/scratches on the flare cone, unmasked anodizing buildup, or misaligned thread concentricity. Always use proper torque specs and aluminum AN wrenches during assembly.

 

 

 

Q4: How does anodizing affect the dimensions and threading of CNC AN fittings?

 

 

A: Type II anodizing typically adds 5–15 µm of surface thickness, while Type III Hardcoat anodizing adds 25–50 µm. Because thread tolerances are tight, non-masked threads must be machined slightly undersized prior to anodizing, or high-precision masking plugs must be used to keep coating off functional threads and sealing cones.

 

 

 

Q5: Can CNC machining or bending cause dimensional errors in AN bent tubes and hose segments?  

 

 

A: Yes, it may happens. But precision CNC tube benders can prevent these errors by using real-time sensor feedback and automatic springback compensation to ensure accurate flare positioning.

 

 

 

Q6 : How are bent AN fittings and tube components safely rotated and secured during CNC machining?

 

 

A: Workpieces are locked using custom-contoured soft jaws, pneumatic clamps, and multi-axis indexable collets. This specialized workholding prevents slippage or tube deformation while allowing full 360-degree rotation for precise port and thread machining.

 

 

 

Disclaimer

 

The technical information and manufacturing advice shared on the VMT website are for general guidance only. While we strive for accuracy, VMT does not guarantee that the processes, tolerances, or material properties mentioned are applicable to every specific project. Any reliance you place on such information is strictly at your own risk. It is the buyer's responsibility to provide definitive engineering specifications for any production orders. Final specifications and service terms shall be subject to the formal contract or quotation confirmed by both parties.