D38999/24 MIL-DTL-38999 Series III Jam Nut Receptacle Connector

Overview

Got it! I will conduct a thorough analysis of your existing webpage, fact-check all information about the D38999-24 connector, and significantly enhance it with accurate technical details, procurement insights, and SEO optimization. The target audience will be engineers and procurement specialists. I will let you know once the improved content is ready.

The D38999/24 connector is a jam-nut mount receptacle in the MIL-DTL-38999 Series III family of high-performance circular connectors. It is engineered for military, aerospace, and other demanding applications requiring robust and reliable interconnections. These Series III connectors are renowned for their durability, high contact density, and excellent resistance to harsh environments (extreme temperatures, vibration, moisture) while providing superior electromagnetic interference (EMI) shielding. The D38999/24 meets stringent military standards, ensuring compatibility and interoperability across equipment from multiple manufacturers. This makes it a go-to solution for engineers designing critical systems and for procurement specialists seeking proven, qualified connectivity hardware.

Key Features

• Shell Style: Jam Nut (Rear Panel) Mount. Installs through a panel hole and is secured with a hex-shaped jam nut from the rear, yielding a low-profile, flush-mount appearance. This design saves front panel space and often includes an O‑ring to seal at the panel interface for environmental protection.
• Coupling Mechanism: Tri‑Start Threaded Coupling. A self‑locking triple‑start thread allows quick mating with just a 360° turn, and an anti‑decoupling ratchet prevents loosening under vibration. This design is 100% scoop‑proof, meaning the shell design prevents misalignment and protects pins from damage during mating.
• Durability: High mating cycle life. Rated for a minimum of 500 mating cycles (connect/disconnect) with no degradation. In practice, certain versions with advanced materials (e.g., composite shells and hardened contacts) are capable of up to 1,500 cycles—ensuring long service life even with frequent use.
• Environmental Resistance: Built to withstand extreme conditions:
  • Temperature: Operates reliably from -65 °C to +200 °C (dependent on materials and plating).
  • Vibration & Shock: Tolerant to high vibration (aircraft/ground vehicle levels) and shock impacts per MIL-DTL-38999 requirements, maintaining connection integrity in combat environments.
  • Sealing: Uses interfacial seals and rear grommets to prevent moisture and dust ingress. When mated, it meets or exceeds IP67 (immersion) sealing levels, keeping out fluids and dirt in harsh field conditions.
  • Corrosion Protection: Designed for salt spray and corrosive atmospheres. Standard aluminum shells with cadmium plating withstand 500 hours of salt fog with no base‑metal exposure. Stainless steel shells offer even greater corrosion resistance (500–1000 hours salt spray) for marine or coastal use. Newer composite shells can endure up to 2,000 hours salt spray while being immune to rust.
  • Fluid Resistance: Compatible with fuels, oils, hydraulic fluid, and cleaning solvents commonly encountered in military and aerospace service.
• EMI/RFI Shielding: Excellent EMI suppression thanks to conductive shell materials and a metal‑to‑metal interface. A 360° shell grounding design provides up to ~65 dB attenuation at high frequencies—protecting signal integrity in electrically noisy environments. This performance meets MIL‑STD‑461 EMI standards when properly installed.
• High Contact Density: Accommodates a large number of contacts in a relatively small circular connector. Insert arrangements per MIL‑STD‑1560 allow anywhere from a few contacts up to over 100 contacts in the largest shells, enabling size and weight savings by consolidating connections.
• Maintenance‑Friendly: Features rear‑release crimp removable contacts, so contacts can be easily inserted or removed with a simple extraction tool if replacement or reconfiguration is needed. This simplifies field maintenance compared to older connectors with fixed solder contacts.

Specifications

Mechanical

• Shell Sizes: Available in shell sizes 9, 11, 13, 15, 17, 19, 21, 23, 25 (size 9 is the smallest, size 25 the largest). Each size supports specific insert arrangements and contact counts.
• Insert Arrangements: Dozens of standardized arrangements per MIL‑STD‑1560, supporting various contact number and size combinations (for example, up to 128 contacts in the largest size 25 shell). This flexibility allows selecting a connector layout optimized for signal, power, and mixed contacts.
• Materials – Shells: Typically machined from high‑strength aluminum alloy with corrosion‑resistant plating. Alternatively, shells can be made from corrosion‑resistant stainless steel or lightweight composite plastic. Some manufacturers even offer marine bronze shells for exceptional corrosion resistance in saltwater environments.
• Finishes (Plating Options): The shells come in several finish classes:
  • Class W: Olive Drab Cadmium plating over nickel on aluminum – traditional mil‑spec finish for superior corrosion resistance (500 hr salt spray) and conductivity, but not RoHS compliant.
  • Class F: Electroless Nickel plating on aluminum – high conductivity and a smooth, durable surface. Moderate salt spray endurance (≈48 hr).
  • Class Z: Black Zinc‑Nickel on aluminum – a RoHS‑compliant alternative with a non‑reflective black finish and excellent corrosion resistance (~500 hr salt spray).
  • Class K: Passivated Stainless Steel – entirely stainless, extremely robust and corrosion resistant (500+ hr salt spray, often over 1000 hr).
  • Class M: Nickel‑PTFE on aluminum – a gray, non‑reflective, low‑friction finish that is RoHS compliant and offers similar performance to cadmium.
• Insulator: Made from high‑grade thermoplastic dielectric material that maintains contact alignment and offers high insulation resistance.
• Contacts: Typically made of copper alloy with gold plating for optimum conductivity and corrosion resistance. Contacts are usually removable crimp style (though solder and PC‑tail versions exist). Options include standard copper and ferro‑nickel alloy hermetic contacts.

Electrical

• Contact Current Ratings: Varies by contact size:
  • Size 22D: ~5 A max
  • Size 20: ~7.5 A
  • Size 16: ~13 A
  • Size 12: ~23 A
  • Size 8: ~46 A
  *(Actual current may be lower in high‑temperature or high‑altitude conditions due to derating.)*
• Operating Voltage: Up to ~500 V_AC (RMS) at sea level. Voltage ratings vary with contact spacing and altitude.
• Dielectric Withstanding Voltage (DWV): Unmated connectors must endure up to 1300 V_AC (RMS) at sea level; derated at altitude (e.g., ~550 V_AC at 50,000 ft).
• Insulation Resistance: ≥ 5,000 MΩ at room temperature (25 °C) under standard humidity.
• Contact Resistance: Very low (a few milliohms), ensuring minimal voltage drop and heating. For example, a size 16 contact may have <5 mΩ when properly crimped.
• EMI Shielding Effectiveness: When assembled with shielded cables and backshells, Series III connectors provide at least 50–65 dB attenuation over frequencies up to 10 GHz.

Environmental

• Temperature Range: Operates from -65 °C to +200 °C (some combinations may be rated to +175 °C).
• Corrosion (Salt Spray) Resistance:
  • Aluminum with cadmium plating (Class W) survives ≥500 hr salt spray.
  • Zinc‑Nickel (Class Z) provides ~500 hr resistance with no galvanic corrosion.
  • Stainless steel (Class K) withstands ≥500 hr (often >1000 hr).
  • Composite shells (Class M) can be tested to ≥2000 hr.
• Vibration & Shock: Endures sine vibration (10–2000 Hz at ~20–30 g) and shock impacts up to 100 g.
• Fluid Resistance: Tested against fuels, oils, hydraulic fluids, coolants, and cleaning solvents.
• Altitude: Fully operational at high altitudes; design prevents arcing in thin atmospheres.

Contact Types and Options

One strength of the D38999/24 (and Series III connectors in general) is its ability to accommodate a variety of contact types:

• Standard Power/Signal Contacts: Copper alloy contacts in sizes 22D, 20, 16, 12, 8, etc., for most power or signal wiring applications.
• High-Power Contacts: Larger contacts (e.g., size 4 or 0) for high-current applications.
• Coaxial Contacts: For RF signals with coaxial construction to maintain impedance (50Ω/75Ω) and low VSWR.
• Twinax/Triax Contacts: For differential pair signals and data buses (e.g., MIL‑STD‑1553B, Ethernet, high‑speed serial).
• Quadrax Contacts: Essentially two twinax pairs in one contact for high-speed data (Gigabit Ethernet protocols).
• Fiber Optic Contacts: Supports optical fiber links per standards (e.g., ARINC 801, MIL‑PRF‑29504) with ceramic ferrules.
• Hermetic Contacts: Glass‑sealed contacts for pressurized or vacuum applications (e.g., sealed enclosures, submarines, space cabins).

Part Number Breakdown

Understanding the D38999/24 part number format is crucial for specifying the exact connector required. The full MIL‑DTL‑38999 Series III part number is structured as follows:

D38999/24  W   A   35   P   N
└───┬───┘ └┬┘ └┬┘ └┬┘ └┬┘ └┬┘  
   │      │   │    │   │   └─ Polarization: N (Normal) or A, B, C, D (alternate key positions)
   │      │   │    │   └──── Contact Type: P = Pin (male); S = Socket (female)
   │      │   │    └──────── Insert Arrangement (number code from MIL‑STD‑1560)
   │      │   └──────────── Shell Size Code (e.g., A = 9, B = 11, …, J = 25)
   │      └──────────────── Material/Finish Class (W, F, Z, K, M)
└──────────────────────── MIL Spec series (D38999) and “/24” indicates Series III Jam Nut Receptacle
      

Example: D38999/24WA35PN denotes a Series III jam‑nut receptacle with a Class W finish, shell size 9 (A), insert arrangement 35, pin contacts, and normal keying. In practice, a receptacle usually uses socket contacts (thus, D38999/24WB35SN is more common).

Mounting and Accessories

Mounting Style (Jam Nut): The D38999/24 receptacle is mounted from the front of a panel or bulkhead with a threaded jam nut tightened from the rear. A gasket or O‑ring under the flange ensures an environmental seal. This rear‑mount style allows the connector to sit flush on the panel while protecting the retention nut.

Termination Methods:

• Crimp Termination: Wires are crimped into removable contacts using standardized crimp tools (e.g., M22520/2‑01) and then inserted into the connector insert.
• Solder Cup Termination: Wires are soldered into contacts integrated into the receptacle (less field‑serviceable).
• PC Tail/PCB Termination: Contacts with printed‑circuit tails allow the connector to be mounted directly on a PCB.

Common Accessories:

• Backshells: Threaded backshells attach to the rear threads to provide cable strain relief, sealing, and EMI continuity. They may be straight or angled and often conform to AS85049.
• Protective Caps: Caps shield the connector face when unmated and may include tether lanyards.
• Sealing Boots: Heat‑shrink boots over backshells add moisture sealing and strain relief.
• Insertion/Extraction Tools: Specialized tools (per MIL‑I‑81969) are used for installing or removing contacts without damage.

Polarization and Keying

To prevent cross‑mating in installations with multiple similar connectors, the D38999/24 offers five keying options (polarization positions): N (Normal), A, B, C, and D.

In the "Normal" position, the connector’s key is in the standard reference orientation. Alternate positions (A–D) rotate the keying to ensure only matching connectors mate—an essential safeguard in complex wiring harnesses.

Applications

• Military and Defense: Communication systems, military radios, ground combat vehicles, aircraft avionics, missile/rocket wiring, radar, surveillance systems, soldier-worn communication hubs, and electronic warfare gear.
• Aerospace: Commercial and military aircraft (flight controls, engine management, sensors), satellites, spacecraft, and launch vehicles.
• Industrial Automation: Robotics, factory automation equipment, and heavy machinery in extreme environments.
• Marine and Offshore: Naval vessels, submarines, ROVs, and offshore oil rigs where corrosion resistance and sealing are critical.
• Transportation and Heavy Equipment: Railway signaling, aerospace ground equipment, emergency vehicles, and heavy trucks subject to severe vibration and weather.

In these applications, failure is not an option—D38999/24’s ruggedness, sealing, and reliability make it indispensable.

Advantages and Benefits

• High Reliability: Meets rigorous MIL‑DTL‑38999 Series III specs for extreme environments and high shock/vibration, ensuring mission‑critical performance.
• Compact, Lightweight Design: Offers high contact density in a smaller form factor compared to legacy connectors, saving space and weight.
• Versatility: A wide range of shell sizes, insert configurations, and contact types, plus various material and plating options, allow tailoring to specific needs.
• Environmental Sealing: When mated (and with proper backshells), connectors achieve IP67+ sealing for operation in dust, rain, salt fog, and immersion.
• EMI/RFI Protection: Metal‑to‑metal coupling and grounding features provide superior electromagnetic shielding.
• Ease of Maintenance: Quick‑thread coupling and removable crimp contacts simplify installation and field repairs.
• Interoperability and Compliance: Open mil‑spec design enables multi‑source supply and long‑term availability while meeting military and aerospace standards.
• Safety and Integrity: Scoop‑proof shells and multiple keying options reduce the risk of mis‑mating, protecting system integrity.
• Supply Stability: Widely adopted and produced by multiple qualified manufacturers, ensuring long‑term support.

Competitor and Market Comparison

When compared with other connector families:

• Versus MIL‑DTL‑5015 Connectors: MIL‑DTL‑5015 are larger, heavier, and support fewer contacts (typically up to 80). In contrast, size 25 D38999 shells can carry up to 128 contacts, offer five keying options, and include features such as self‑locking coupling and scoop‑proof design.
• Versus MIL‑DTL‑26482 Connectors: Although MIL‑26482 connectors use bayonet coupling for quick disconnect, they have lower contact density and environmental ratings. Series III D38999 connectors deliver higher temperature ratings (up to +200 °C) and better EMI shielding.
• Versus Other MIL‑Spec/Industrial Connectors: While some alternatives may offer IP67 sealing or high‑density arrangements, few provide the complete package of extreme temperature performance, robust shock/vibration certification, and full MIL‑STD compliance.

In summary, the D38999/24 (Series III) stands out with its high contact density, multi‑keyed scoop‑proof design, and proven MIL‑spec performance—making it the connector of choice for new military and aerospace designs.

Note that the 38999 Series includes multiple variants (I, II, III, IV) to suit different needs. Series III, using threaded coupling, is the most popular for its robustness and ease‑of‑use.

Procurement and Sourcing Considerations

• Authorized Manufacturers and Part Numbers: MIL‑DTL‑38999 connectors are produced by several QPL‑approved suppliers (e.g., Amphenol Aerospace, TE Connectivity, ITT Cannon, Glenair). Always use the full MIL‑DTL‑38999 part number to ensure quality and compliance.
• Lead Times and Availability: Lead times can vary from 4–6 weeks up to 26 weeks or more. Plan ahead and consider dual‑sourcing to mitigate supply chain risks.
• Alternate Finishes for Compliance: Be aware of RoHS/REACH requirements. For RoHS compliance, opt for Class Z (Black Zinc‑Nickel) or Class M (Nickel‑PTFE) finishes instead of Class W (cadmium plated).
• Cost Considerations: Stainless steel (Class K) and composite (Class M) options may be pricier than aluminum versions. Evaluate cost versus performance and compliance needs.
• Supply Chain and Counterfeit Mitigation: Procure only from trusted, authorized distributors to avoid counterfeit parts and ensure full traceability.
• Documentation and Certification: Request Certificates of Conformance, test reports, and material certifications as needed—especially for aerospace applications.
• Alternatives and Second Sources: Dual‑source critical components by listing two approved manufacturers in your specifications.
• Lifecycle and Obsolescence: MIL‑DTL‑38999 connectors have a long life. Monitor QPL updates and potential plating changes (e.g., cadmium vs. RoHS‑compliant options).
• Handling and Installation: Ensure proper assembly using correct torque specs and insertion tools. Some connectors are sold without contacts, so verify that connector kits include all necessary components.

Call to Action – Next Steps for Procurement:

• Compile the full specification (shell size, insert arrangement, contact type, plating) into the complete part number.
• Request a quote from an authorized distributor or manufacturer.
• Check stock availability and consider acceptable equivalents if needed.
• Consult technical support for cross‑references and 3D models.
• Place orders early to accommodate long lead times and ensure compliance.

Conclusion

The D38999/24 Jam Nut Receptacle is a versatile, high‑performance connector exemplifying modern mil‑spec design. Combining rugged construction, environmental resilience, and high configurability, it is ideally suited for mission‑critical applications in military, aerospace, and industrial systems.

Its technical specifications—from materials and electrical ratings to sealing and durability—coupled with its interoperability and multi‑source supply make the D38999/24 a proven, reliable solution for secure and dependable connections in even the most demanding environments.

Whether you are an engineer designing next‑generation aircraft or a procurement specialist securing components for fleet maintenance, the D38999/24 delivers the performance and long‑term supply stability needed for critical systems.