Skip to Content
  1. All products
  2. Plugs and Caps
  3. AN929-4 - AN Fitting Aluminum Threaded Cap
  4. Plugs and Caps
Pricelist: - Pricelist
Pricelist: - Pricelist
AN929-4 - AN Fitting Aluminum Threaded Cap

AN929-4 - AN Fitting Aluminum Threaded Cap

(0 review)
$ 6.57 $ 6.57

AN929-4 – AN Fitting Aluminum Threaded Cap

Available now on the Airparts.aero Marketplace.

The AN929-4 is a precision-engineered, aerospace-standard protective cap designed to seal the external threads of flared tube fittings or male AN connectors. Manufactured to the strict requirements of the Army-Navy (AN) Aeronautical Standard, this cap is a critical component for maintaining the integrity of aircraft fluid systems during maintenance, shipping, or storage. By providing a secure, threaded seal, the AN929-4 prevents the ingress of dust, moisture, and foreign object debris (FOD) into high-pressure hydraulic, fuel, or oil lines, which could otherwise lead to system contamination or component failure.

Constructed from high-strength 2011-T3 or 6061-T6 aluminum alloy, the AN929-4 is blue-anodized for easy identification as an aluminum component (distinguishing it from steel or stainless variants). The cap features a standard 7/16-20 UNJF-3B internal thread, optimized for use with -4 size (1/4 inch) flared fittings. Its robust construction allows it to be used as a pressure-sealing cap in certain low-to-medium pressure applications, ensuring that the critical $37^\circ$ mating surfaces of flared fittings remain pristine and free from mechanical scoring.

Key Features

  • Aerospace-Grade Aluminum Alloy: Manufactured from 2011-T3 or 6061-T6 aluminum, providing an excellent strength-to-weight ratio and natural resistance to atmospheric corrosion.

  • Blue Anodized Finish (MIL-A-8625): The electrolytic passivation process provides a hard, wear-resistant surface that prevents galling during installation and color-codes the part for aluminum material identification.

  • Precision UNJF-3B Threads: Features "J" series threads with a controlled root radius to increase fatigue life and ensure a high-tolerance fit on male AN-37° flared fittings.

  • Knurled External Surface: Designed with a diamond-pattern knurl to allow for rapid, hand-tightened installation and removal by technicians, even in oily or confined environments.

  • FOD Prevention Architecture: Engineered to seal the fluid path completely, protecting the critical sealing cone of the mating fitting from nicks, scratches, and environmental contaminants.

Technical Specifications

  • Part Number: AN929-4

  • Standard: AS929 (Superseding AN929)

  • Fitting Size: -4 (For 1/4" OD Tubing)

  • Thread Size: 7/16-20 UNJF-3B

  • Material: Aluminum Alloy (2011-T3 or 6061-T6)

  • Finish: Blue Anodize per MIL-A-8625, Type II

  • Weight: Approx. 0.01 lbs (4.5 grams)

  • Mating Fitting: Interfaces with any male $37^\circ$ AN/JIC flared fitting.

  • Pressure Rating: Suitable for system storage and low-pressure static testing (Verify specific PSI limits per AS929 data sheet).

Aircraft Compatibility

  • General Aviation (GA): Universal application across Cessna, Piper, Beechcraft, and Mooney fuel and hydraulic systems.

  • Business & Commercial Jets: Used in non-flight-critical fluid line capping for Gulfstream, Bombardier, and Boeing maintenance.

  • Experimental Aircraft: A staple for RV-series and Kitfox builders for fuel system plumbing and brake line protection.

  • Note: Refer to the specific Aircraft Maintenance Manual (AMM) for instructions on using threaded caps versus plastic dust caps in pressurized vs. unpressurized systems.

Applications

The AN929-4 is utilized for Fluid System Protection & Containment. Its primary roles include:

  • System Maintenance: Sealing open lines during component replacement (e.g., fuel pumps or oil coolers) to prevent fluid loss and contamination.

  • Pressure Testing: Acting as a terminal plug for low-pressure leak checks of fuel and vent lines.

  • Logistics & Shipping: Protecting the threads of expensive overhauled components during transit to the hangar.

Why Choose AN929-4?

Choosing a genuine MIL-SPEC AN929-4 cap ensures that the metallurgy and thread tolerances are consistent with the fittings they protect. Unlike plastic caps, the aluminum AN929-4 will not degrade or "shed" particles when exposed to aggressive aerospace fluids like Skydrol, Avgas, or turbine oil. The use of an aluminum cap on an aluminum fitting also prevents galvanic corrosion and ensures that the thread coefficient of friction remains predictable, preventing over-torque damage to the male fitting threads.

The AN929-4 is designed to interface with the JIC/AN $37^\circ$ flare geometry. The internal threads of the cap are cut to the UNJF-3B standard, which specifies a tighter tolerance and a larger root radius than standard UNF threads. This design reduces stress concentrations at the thread roots, which is vital in high-vibration aerospace environments. While the cap is primarily a protective device, it achieves a mechanical seal through the contact between the internal flat of the cap (or an optional copper crush washer) and the apex of the male fitting's cone. Because the cap is made from precipitation-hardened aluminum alloy, it possesses a thermal expansion coefficient similar to the aluminum fittings it typically protects, ensuring the seal remains stable during the extreme temperature gradients ($100^\circ\text{C}$ to $-55^\circ\text{C}$) encountered in flight.

Note: This is a protective hardware component. While threaded aluminum caps provide superior protection over plastic variants, they should not be used as permanent high-pressure plugs unless specified by the airframe manufacturer. Inspect the internal threads for debris or metal shavings before installation. Hand-tighten to prevent cross-threading; if a wrench is required, ensure the torque does not exceed the limits for aluminum -4 fittings as defined in FAA AC 43.13-1B.

Documentation

Description:   CAP
Part number:   AN929-4
Alternate part number:   AN929-4D, 946-29-15-803, 454-173
Industry Standards/Certification:   AN929

Cap Assembly - Tube Outer Dia: 1/4", Flared Tube Fitting, Pressure Seal, Aluminum


This part is used on the following aircraft:

  1. Bombardier Challenger 601
  2. Bombardier Challenger 604
  3. Bombardier Challenger 605
  4. Bombardier Learjet 40
  5. Bombardier Learjet 45
  6. Bombardier Learjet 55
  7. Bombardier Learjet 60 - all variants
  8. Dassault Falcon 2000 all variants
  9. Dassault Falcon 7X
  10. Dassault Falcon 900 all variants
  11. Embraer Legacy 600-650
  12. Gulfstream G-IV/GIV-SP/G-400/G-450/G-300
  13. Gulfstream G-V/G-V-SP/G-550/G-500
  14. Pilatus PC-12
  15. Piper Aircraft PA-42 Cheyenne
  16. Textron Aviation Beechcraft King Air 100 - all variants
  17. Textron Aviation Beechcraft King Air 200 - all variants
  18. Textron Aviation Beechcraft King Air 300 - all variants
  19. Textron Aviation Beechcraft King Air 90 - all variants
  20. Textron Aviation Beechcraft Premier
  21. Textron Aviation Bell 206 Jetranger/Longranger
  22. Textron Aviation Cessna 500 Citation I-ISP
  23. Textron Aviation Cessna 510 Citation Mustang
  24. Textron Aviation Cessna 525 Citation Citationjet
  25. Textron Aviation Cessna 550 Citation I-II-Bravo
  26. Textron Aviation Cessna 560 Citation V-Ultra-Encore-Excel-XLS
  27. Textron Aviation Cessna 650 Citation III-IV-VI-VII
  28. Textron Aviation Cessna 680 Citation Sovereign
  29. Textron Aviation Cessna 750 Citation X
  30. Textron Aviation Hawker 400-400XP
  31. Textron Aviation Hawker 800
  32. Textron Aviation Hawker 800XP-850XP
  33. Textron Aviation Hawker 900XP



Between AirParts' branded hardware products, and our Seller's hardware offerings, we have hundreds of thousands of hardware parts in stock.