MIL-DTL-38999 contacts are critical components within the D38999 series connectors, engineered for robust performance in severe environments. They ensure reliable electrical connections in military, aerospace, marine, industrial, and other demanding applications, offering a range of types and sizes to accommodate different electrical requirements.
Contact Types
Crimp Removable Contacts:
Standard contacts crimped onto wires and inserted or removed using specialized tools.
Facilitate easy installation and field repairs.
Solder Contacts:
Permanently soldered to wires, ideal for fixed or high-vibration applications.
Provide a secure and durable connection.
Coaxial Contacts:
Designed for RF signal transmission while maintaining characteristic impedance.
Utilized with specific coaxial as specified in MIL-DTL-39029.
Twinax/Triax Contacts:
Support balanced differential signal transmission with high noise immunity.
Common in data bus systems like MIL-STD-1553B and high-speed Ethernet applications.
Fiber Optic Contacts:
Enable optical data transmission, immune to electromagnetic interference.
Accommodate single-mode and multimode fibers.
Thermocouple Contacts:
Made from thermocouple alloys like chromel, alumel, iron, and constantan.
Used for accurate temperature measurements without introducing additional thermoelectric voltages.
Power Contacts:
Larger contacts capable of carrying higher currents for power distribution.
Available in sizes like 8, 4, and size 0 for currents up to 150 A.
Shielded Contacts:
Provide electromagnetic shielding for individual contacts.
Used in applications requiring minimal signal interference.
PCB Tail Contacts:
Designed with solder tails for direct mounting onto printed circuit boards.
Simplify integration into electronic assemblies.
Filter Contacts:
Incorporate filtering components like capacitors or ferrites.
Reduce electromagnetic interference (EMI) and radio frequency interference (RFI).
Contact Sizes and Specifications
Electrical Specifications
Contact Size
Wire Size (AWG)
Current Rating (A)
Max Contact Resistance (mΩ)
Service Rating (Voltage)
23
28–22
5
73
M (500V)
22D
28–22
5
14.6
M (500V)
20
24–20
7.5
7.3
M (500V)
16
20–16
13
3.8
M (500V)
12
14–12
23
3.0
I (1,000V)
8
8
46
1.5
II (1,500V)
4
4
80
0.7
—
0
0
150
0.5
—
Materials and Plating
Contact Materials:
Copper Alloys:
Common base materials include high-conductivity copper alloys such as beryllium copper, phosphor bronze, and brass.
Provide excellent electrical conductivity and mechanical strength.
Thermocouple Alloys:
Contacts made from specific thermocouple materials like chromel, alumel, iron, and constantan.
Used in thermocouple circuits to prevent introduction of parasitic thermoelectric voltages.
Stainless Steel:
Used in specialized contacts for high-temperature or corrosive environments.
Offers enhanced mechanical strength and environmental resistance.
Plating Options:
Gold over Nickel:
Standard plating providing excellent corrosion resistance, conductivity, and durability.
Gold thickness typically ranges from 50 to 100 microinches over 50 microinches of nickel underplate.
Silver Plating:
Used in high-current applications due to silver's superior conductivity.
Offers good solderability and conductivity but less corrosion resistance than gold.
Tin or Tin-Lead Plating:
Used in some solder contacts for improved solderability.
Not typically used in crimp contacts due to potential for oxidation.
Selective Plating:
Plating applied only to critical areas like contact mating surfaces.
Reduces cost while maintaining performance where needed.
Composite Plating:
Combines multiple layers or materials to enhance performance.
Examples include gold flash over palladium-nickel for increased wear resistance.
Mechanical Specifications
Contact Retention:
Contacts are retained within the connector insert using retention clips or tines.
Retention mechanisms meet or exceed MIL-DTL-38999 requirements for contact retention forces.
Minimum Retention Force:
Size 22D Contacts: ≥ 9 pounds-force (40 N)
Size 20 Contacts: ≥ 15 pounds-force (67 N)
Size 16 Contacts: ≥ 25 pounds-force (111 N)
Size 12 Contacts: ≥ 30 pounds-force (133 N)
Size 8 Contacts: ≥ 40 pounds-force (178 N)
Size 4 Contacts: ≥ 50 pounds-force (222 N)
Mating Cycles:
Contacts are rated for a minimum of 500 mating cycles under normal conditions.
With proper care and maintenance, contacts can withstand up to 1,500 mating cycles.
Factors affecting mating cycles include environmental conditions, contamination, and mechanical wear.
Engagement and Separation Forces:
Maximum Engagement Force per Contact:
Size 22D Contacts: ≤ 12 ounces-force (3.33 N)
Size 20 Contacts: ≤ 12 ounces-force (3.33 N)
Size 16 Contacts: ≤ 16 ounces-force (4.44 N)
Size 12 Contacts: ≤ 24 ounces-force (6.67 N)
Minimum Separation Force per Contact:
Size 22D Contacts: ≥ 0.5 ounces-force (0.14 N)
Size 20 Contacts: ≥ 1 ounce-force (0.28 N)
Size 16 Contacts: ≥ 1.5 ounces-force (0.42 N)
Size 12 Contacts: ≥ 2 ounces-force (0.56 N)
Insertion and Removal Tools:
Contacts are designed for insertion and removal using appropriate tools without causing damage.
Tool usage ensures consistent insertion depth and proper seating within the connector.
Vibration and Shock Resistance:
Contacts maintain electrical continuity under high vibration (up to 2000 Hz) and shock conditions as specified in MIL-DTL-38999.
Designed to prevent fretting corrosion and micro-motion that could degrade performance.
Operating Temperature Range:
Mechanical performance is maintained across the temperature range of -65°C to +200°C, depending on materials and finishes.
Consideration of thermal expansion coefficients ensures mechanical integrity at temperature extremes.
Dimensional Tolerances:
Contacts are manufactured to precise tolerances to ensure proper fit and function.
Critical dimensions adhere to the specifications outlined in MIL-DTL-39029 slash sheets.
Contact Alignment:
Contacts feature lead-in chamfers and are supported by the connector inserts to facilitate alignment during mating.
Prevents bending or damage to contacts during assembly and use.
Mechanical Durability:
Contacts are designed to withstand mechanical stresses encountered during installation, maintenance, and operation.
Materials and coatings are selected for abrasion resistance and longevity.
Environmental Specifications
Temperature Range: -65°C to +200°C, depending on materials and connector class.
Durability: Withstands severe vibration and shock per EIA-364 test methods.
Corrosion Resistance: Plating provides protection against salt spray and chemicals.
Sealing: Contacts and connector seals prevent moisture and contaminant ingress.
Part Number Breakdown
MIL-DTL-38999 contacts are identified by part numbers following the MIL-DTL-39029 specification (also known as SAE-AS39029), encoding detailed information about the contact's type, size, material, and characteristics.
General Format
M39029/XX-YYY
│ │ └─ Dash Number: Specific contact variant.
│ └───── Slash Sheet Number: Defines contact type and size.
└───────────── Military Specification Identifier.
The part number consists of:
M39029: Military specification number for contacts.
/XX: Slash sheet number specifying contact type, size, and application.
-YYY: Dash number identifying specific variants like wire size and plating.
Example Breakdown
Example 1: M39029/58-360
M39029: Military specification for electrical contacts.
/58: Slash sheet for size 22D pin contacts, crimp removable, for MIL-DTL-38999 connectors.
-360: Variant accommodating wire sizes 22 to 26 AWG, with specified features.
Example 2: M39029/57-354
M39029: Military specification for electrical contacts.
/57: Slash sheet for size 22D socket contacts, crimp removable.
-354: Variant accommodating wire sizes 22 to 28 AWG, with specified plating and design.
Understanding Slash Sheets
Each slash sheet (/XX) corresponds to a detailed specification within MIL-DTL-39029, defining:
MIL-DTL-38999 contacts are essential for the performance and reliability of connectors in demanding environments. Their variety, precise specifications, and compliance with military standards make them suitable for applications where failure is not an option. By understanding their characteristics and following best practices in selection, installation, and maintenance, optimal performance and longevity of critical systems can be ensured.