MIL-DTL-38999 Series III Military Circular Cable Assembly

Overview

A military mil dtl cable built on MIL-DTL-38999 Series III is the default answer when a harness has to survive vibration, salt air and a wide temperature swing and still be serviceable in the field. It belongs to the circular connector family specified for exactly that job. Series III is the threaded member of the family: a tri-start coupling that pulls the two halves together and locks, with scoop-proof shells so a pin cannot be bent by a plug that is offered up slightly off axis. Shell sizes run from 09 to 25, insert arrangements are selected from MIL-STD-1560, and we wire to the arrangement you name rather than to a house standard. We build and verify to your drawing; we do not claim certification to the detail specification.

Key Specifications

Four series, one part number prefix: which one is on the drawing?

MIL-DTL-38999 is a family rather than a part, and the series letter changes the coupling, the silhouette and, in practice, whether it will mate with the receptacle already fitted to your box. Series III is the one most new designs specify, largely because the threaded coupling gives both a positive lock and a low-resistance shell-to-shell path for EMI grounding.

Reading the callout before you send it to us

Most RFQs for this family arrive as a part number rather than a description, which is good, because the number encodes everything we need. If you only have a NSN or a drawing, the fields below are the ones we will ask you for. Where a field is unclear we will come back to you rather than guess, because an alternate keying position is invisible until two halves will not mate.

What the environmental clauses actually ask for

The reason this family costs what it costs is not the contacts, it is the qualification: salt spray, vibration, shock and thermal cycling, plus shell-to-shell conductivity and EMI shielding effectiveness. Those are real requirements with real test methods behind them, and they belong on your drawing rather than in a marketing sentence. Tell us the exposure hours, the vibration profile and the temperature range you need met, and we will tell you honestly which of them we can verify in house and which need an external laboratory.

• Salt spray – the exposure hours and the plating system go together; a zinc-cobalt or zinc-nickel shell and a cadmium shell do not behave the same way in a Fog chamber.
• Vibration – the profile matters more than the number. Random and sinusoidal profiles expose different weaknesses.
• Thermal cycling – the extremes plus the dwell time, because it is the cycling that loosens a contact rather than the temperature itself.
• Sealing – mated ingress rating plus whether the backshell and the jacket are part of the sealed path.

Construction

• Series III shells in the size and plating you nominate, with the keying position on the drawing.
• Contacts crimped on the correct die for the size, inserted and removed only with the proper tool.
• Shielded bundle with the braid terminated 360 degrees into the backshell, not pigtailed.
• PUR or FEP jacket depending on the temperature and fluid exposure.
• Overmolded or heat-shrunk backshell boots with strain relief tied into the shell.

What we need from you to quote

1. The full connector callout for both ends, including keying and plating.
2. The insert arrangement per MIL-STD-1560, and which cavities are populated.
3. The pinout, or the schematic the harness has to match.
4. Jacket and shielding, with the temperature and fluid exposure.
5. Length and quantity, plus whether this is a prototype or a production order.

Typical applications for this military mil dtl cable

• Avionics and ground support equipment where a threaded, EMI-grounded coupling is mandatory
• Radar, radio and shelter interconnects, alongside a 38999 high-speed harness
• Vehicle and shipboard harnesses exposed to salt air, paired with a MIL-DTL-5015 circular power assembly
• Test and measurement racks that have to survive a transport case, next to a railway rolling stock harness
• Unmanned platforms where weight and vibration both matter, with a lightweight UAV wire harness on the airframe side

Workmanship and testing

MIL-DTL-38999 Series III Military builds are made to IPC/WHMA-A-620 Class 3 workmanship inside an ISO 9001 system, over a 32 to 12 AWG range. continuity and pinout are verified on each MIL-DTL-38999 assembly before packing, and seal checking is quoted whenever an ingress rating is on the drawing.

Material declarations against RoHS and REACH are issued per project, alongside the dimensional and electrical reports agreed at quotation; see certifications, compliance and material declarations. Where your drawing names a UL style or another approval, the build follows your drawing and ships with the supporting document rather than a claim of our own. Overmold tooling for this part is designed and cut in our own tool room under in-house mold making and overmold tooling, so the tool belongs to your program and a revision is a machining job rather than a new negotiation. Related reading: how we build and document first articles.

Custom builds and ordering

For MIL-DTL-38999 Series III Military builds, prototypes run from 1 to 50 pcs with a 3 working day turnaround. Volume orders begin at 500 pcs and ship 14 working days after approval. Tooling not already held adds around 10 working days. OEM and ODM MIL-DTL-38999 work ships under your part number and labeling, and material certificates plus first-article reports are available.

Related military harnesses

• 38999 High-Speed Harness for Radar and Airborne Ethernet
• MIL-DTL-5015 Circular Power Cable Assembly
• Micro-D Shielded Jumper, MIL-DTL-83513
• Lightweight UAV Wire Harness
• Railway Rolling Stock Harness

Full range: custom wire harnesses.

Frequently Asked Questions