MIL-DTL-38999 Circular Connectors

Connectors marked only as "38999 type" are sold commercially. They are not the same thing as MIL qualified product and cannot be used where the procurement requirement is MIL-DTL-38999. There is a second distinction inside the genuine lines as well — the standard range covered by the specification, and options the manufacturer supplies under its own designation only. The Amphenol catalog states that PCB terminations, high-density (HD) inserts, and EN3645 Quadrax and grounded arrangements are not QPL certified. Where a procurement document calls for QPL-listed product those options cannot be used, so send us the P/N and we will confirm whether it is standard range or an Amphenol designation.

Series III (Tri-Start) is the one most often specified in defense procurement. If you are not sure which series you have, send us the P/N from the drawing and we will identify it. MIL-DTL-38999 is built by several divisions within Amphenol, so the same series carries different product line names — Amphenol Aerospace calls it Tri-Start, Amphenol Socapex calls it TV and CTV. Parts built to the same specification mate with each other, but drawings sometimes call out a particular manufacturer's P/N, so passing the specified P/N to us exactly is the more accurate route. For a new design where size and weight are the constraint and no specification is imposed, Amphenol's subminiature 2M line is also worth considering — but 2M is not MIL-DTL-38999 qualified, so it cannot substitute where the drawing calls out D38999.

Specification

MIL-DTL-38999 Series III

Qualified

MIL-DTL-38999 Rev. J

Coupling

Triple-start thread

Shell material

Aluminum · Stainless steel · Class K firewall · Composite

High-vibration option

Clutch-Lok

Contact sizes

22D · 20 · 16 · 12 · 10 · 8 · 4 · 0

Specification

MIL-DTL-38999 Series I (LJT) · Series II (JT)

Also meets

MIL-C-27599

Coupling

Bayonet lock · 5 key/keyway

Contact count

2 – 128 contacts

Contact sizes

8 · 10 · 12 · 16 · 20 · 22 · 22D · 22M

Contact plating

Gold, 50 μin minimum (100 μin option)

Shell styles include wall mounting receptacle, box mounting receptacle, straight plug, jam nut receptacle, 90° plug, and solder mounting receptacle.

• Shrink boot adaptorDetails · tap to expand

  Used to finish unshielded cable with a heat-shrink boot. It has a groove for the boot lip to catch and enough room inside to route the cable with slack. A heat-shrink boot is one way to get environmental protection and strain relief together, and using the matching adaptor is what keeps later repair possible.

• Crimp ring adaptorDetails · tap to expand

  Used when a heat-shrink boot is wanted and the shield (screen) has to be terminated as well. The ring is crimped onto the backshell body, capturing the shield between them.

• Band lock adaptorDetails · tap to expand

  Another way to terminate the shield. A tempered band is tightened with a dedicated tool, and a heat-shrink boot can be fitted over it. Both crimp ring and band terminations have low DC resistance.

• Pre-shield adaptorDetails · tap to expand

  Comes with a length of braid already attached. It overlaps the cable braid for 360° shield contact, and the termination work is fast.

• Other accessoriesDetails · tap to expand

  Quick clamps, strain relief clamps, grommet nuts, SQ adaptors, and ramp thread adaptors. Where saving weight comes first and only strain relief is needed, the clamps and nuts are the right choice.

M85049 is a specification that several Amphenol divisions build together (Aerospace · PCD · Socapex · Canada · Air LB), so the P/N alone does not identify which division made a given part. We therefore confirm the supply route on a P/N basis when quoting. ADMTEC keeps M85049 backshells and 2M shrink boots in Korean stock — send the connector P/N together with the cable outer diameter and we will confirm the matching shell size and cable exit size.

Contact sizes (PCB termination range)

22D · 20 · 16

Tail diameter

Varies by P/N — see the table below

Tail length

0.15" · 0.25" · 0.35"

Plating

Gold plated or pre-tinned

RoHS

Compliant (exemption 6(c) applied)

• ⚠️ Tail diameter differs by P/N even at the same sizeDetails · tap to expand

  Among size 20 contacts the "10-497640" line has a 0.019" tail diameter, while "10-497596-055" has 0.025". Designing the board from the size marking alone can leave the hole dimension wrong, so always confirm on a P/N basis.

• 🔴 These are not AS39029 listed partsDetails · tap to expand

  If your procurement document requires AS39029 or QPL-listed contacts, PCB tail contacts cannot meet it — in that case we will point you to crimp contacts instead. Tell us the required specification first and we will confirm which one applies. Amphenol keeps AS39029 contacts (Mil-Spec Contacts) and PCB contacts as separate product families. AS39029 presumes crimp termination, and terminating straight into a board is not a termination method that specification covers.

• The coaxial contact 21-033592-031 is a different partDetails · tap to expand

  It is not a PCB contact but a matched-impedance coaxial contact. Its mating socket is 21-033591-031, and the manufacturer states that 21-033591 series sockets mate only with 21-033592 series pins, so do not mix pins and sockets across families when ordering. It is 75 Ω, contact size 8, pin, and is used with 179DT · Belden 1855A · VDM230 cable. It applies to Series I (LJT-R), II (JT-R), and III (TV-R) alike.

The board design usually comes first, and once contact size and tail length are fixed the board hole diameter follows from them. Send us the connector P/N, the insert arrangement, and the tail length you need, and we will confirm the right contact.