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DEFENSE · CONNECTORS

What Is MIL-DTL-38999?

MIL-DTL-38999 is the US military specification for high-density, environmentally sealed circular connectors. It defines four series of connector, with bayonet, threaded and breech-lock coupling, used for power, signal and data on aircraft, military vehicles and rugged computers.

01

The Short Answer

MIL-DTL-38999 is a US Department of Defense specification for miniature, high-density circular connectors that stay sealed against dust, water and fluids. The same family covers many shell sizes and contact arrangements, so one standard handles power, low-speed signals and high-speed data on a single platform.

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    Series I Bayonet coupling with long, scoop-proof shells that protect the contacts while mating.
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    Series II Low-profile bayonet coupling where height behind a panel is limited.
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    Series III Triple-start threaded coupling, the most widely specified series, resistant to vibration and quick to mate.
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    Series IV Breech-lock coupling for fast, positive mating with gloved hands.
02

Why It Matters

Rugged computers for defense and aerospace use MIL-DTL-38999 connectors because they keep their seal and contact integrity through shock, vibration and temperature cycling, where commercial connectors can loosen or let moisture in. Forecr’s MILBOX-AGX, for example, takes its power through a MIL-DTL-38999 connector, as described in our Airbus ISR drone case study. For sealed industrial equipment that does not need a military specification, M12 connectors are the more common choice.