MIL-DTL-38999 connectors, formerly designated as MIL-C-38999, comprise four primary series: Series I, Series II, Series III, and Series IV. Each series is engineered with a distinct coupling method, tailored core advantages, and specific application scenarios to meet the rigorous demands of military and aerospace systems.
| Series | Coupling Method | Core Advantages | Typical Applications |
| Series I | Bayonet (1/4-turn) | Enables fast blind mating, delivers reliable anti-vibration performance, and meets IP67 environmental protection standards | Avionics, tactical communication terminals, military ground vehicle electronics |
| Series II | Low-profile bayonet | Features ultra-compact and lightweight design, optimized for high vibration resistance in space-constrained setups | Unmanned Aerial Vehicles (UAVs), portable military instruments, miniaturized avionics subsystems |
| Series III | Tri-start Stub-ACME thread (360° self-locking) | Boasts full EMI/RFI shielding, IP68 protection, 500-hour salt spray resistance, and wide temperature tolerance (-65°C to +200°C); the most widely adopted series | Aerospace propulsion systems, satellite communication equipment, high-speed data link interfaces, naval shipboard electronics |
| Series IV | Breech-Lok latching (1/4-turn with positive locking) | Provides tactile, visual and audible mating confirmation, extreme anti-vibration and shock resistance, and prevents accidental disconnection | Missile guidance systems, heavy-duty weapon platforms, tactical missile launch systems, high-shock industrial equipment |
