Aerospace Circular Connectors: MIL-DTL-38999 and Its Relatives

Updated October 12, 2026

The circular families and where each one shows up

Four military families cover most circular connectors on aircraft, launch vehicles, spacecraft and ground support equipment. MIL-DTL-38999 is the default for new high-density designs; the others persist because the hardware they mate with is still flying or still being built.

NASA's parts selection list notes that Series I, II, III and IV of MIL-DTL-38999 are not intermateable with each other, so a mate on a drawing is always a series-specific choice. For how these parts fit into a finished assembly, see the wire harness sourcing guide.

The specifications that govern them, and their status

The general specification sets performance and test requirements; slash sheets (D38999/20, /26 and so on) and MS sheets define each part. Status below is as listed on EverySpec and the issuing body as of October 2026; confirm in DLA ASSIST before you write a new drawing.

The practical point: a status of active on the general specification does not mean every slash sheet or insert arrangement is open for new design. Read the note on the sheet itself.

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How a D38999 part number is built

A Series III or IV QPL part number reads left to right as specification, slash sheet, class (finish), shell size code, insert arrangement, contact type and key position. Glenair's QPL ordering page uses this sample, which we decode with its definitions:

Series I and II parts use MS numbers instead (MS27466, MS27473, MS27474 and others), with the class and finish carried as separate letters. NASA lists the Series I and II field order as MS number, class, shell size, finish, arrangement, contact type and polarization. Never shorten either format on a PO. An arrangement number means nothing without its shell size, and an omitted key letter is a different part.

Manufacturers also sell equivalent connectors under their own commercial part numbers, sometimes with options the QPL number does not carry. Those are not interchangeable on a drawing that calls the D38999 number unless your engineering authority approves the substitute.

Finish classes: cadmium, nickel, zinc-nickel and the space problem

The class letter is the most consequential choice after the series, because it sets corrosion resistance, temperature limit, conductivity and whether the part is allowed on your vehicle at all. These definitions come from Glenair's D38999/20 QPL page and Amphenol's zinc-nickel announcement.

Corrosion versus temperature. Electroless nickel on aluminum (F) runs hotter but carries a 48 hour salt spray rating, while cadmium (W) and zinc-nickel (Z) carry 500 hours with a lower ceiling. On a launch pad in salt air, that difference matters for GSE and vehicle connectors that sit unmated.

Space hardware. NASA's parts selection list prohibits cadmium plating and zinc plating on EEE parts and associated hardware unless a project waiver is approved by materials and parts engineering. The stated reasons are sublimation in vacuum, with conductive deposits that can short circuits, and metal whisker growth. That rules out W, J and Z classes for most flight electronics and points spacecraft buyers to nickel finishes. Class G exists for space use; Glenair notes it must be ordered with its outgassing modification code to meet the thermal vacuum outgassing requirement.

Hexavalent chromium. Olive drab cadmium finishes are commonly described by distributors as chromate over cadmium. If your contract carries DFARS 252.223-7008 (Jan 2023), which bars deliverables containing hexavalent chromium above 0.1 percent by weight unless the contracting officer specifies otherwise, ask the manufacturer what the finish contains and get the authorization question answered before release.

Finish selection on the shell is covered here. Coating processes in general are covered in the coatings library.

Mating cycles, inserts, accessories and outgassing

Standard Series III pin and socket contacts are rated for 500 mating cycles; the H and J contact codes are rated for 1,500. Connectors that mate on every test run, such as GSE and test cable interfaces, are the place to ask for the higher rating or to put a saver connector in the line.

• Contacts. NASA notes that 38999 connectors are supplied with contacts, and replacement contacts are bought to the contact specification, now SAE AS39029. Our contacts, backshells and terminals page covers those.
• Backshells and seal plugs. Strain relief backshells are bought separately to AS85049, and NASA recommends MS27488 seal plugs in unused contact cavities so the grommet seal still works.
• Outgassing. For contamination-critical hardware, NASA describes processing that typically includes a bakeout at 125 C under vacuum, preferably at 10 to the minus 6 torr or better, replacement of the factory lubricant with a low outgassing one, and sometimes removal of ink color bands from contacts. Some QPL makers sell low outgassing versions under commercial part numbers.
• Arrangement availability. NASA advises checking the current QPL for availability, because many insert arrangements exist on paper but are not stocked or built often.

QPL and QPD sourcing

Military connectors are qualified products: only manufacturers listed on the Qualified Products List for that specification can sell the part under the military part number. DLA publishes those listings in its Qualified Products Database (QPD), searchable by specification and slash sheet.

Three checks matter before a buy:

1. Confirm the manufacturer is qualified for that slash sheet and class, not only for the specification in general. Qualification is often granted by series, style and finish.
2. Confirm the source is the manufacturer or its authorized or franchised distributor for that product line. Distributors frequently assemble 38999 connectors from qualified piece parts under the manufacturer's authorization, so ask how the part was assembled and under whose certification.
3. Check whether the sheet or arrangement is marked inactive for new design. You can still buy it for an existing drawing, but expect fewer makers and longer waits.

What to put on the purchase order

• Full part number exactly as on the drawing, including class, shell size code, arrangement, contact type and key letter.
• Specification and revision, and the slash sheet revision if your program controls it.
• Approved manufacturers, or a statement that any current QPL source is acceptable.
• Source requirement: manufacturer or its authorized or franchised distributor, with the distributor's certificate of conformance and the manufacturer's certificate where provided.
• Lot or date code traceability recorded on the certificate and on the package label.
• Contacts included or less contacts, and any contact part numbers bought separately.
• Backshell, seal plugs, dust caps and protective covers as separate lines.
• Finish restrictions: no cadmium or zinc on space hardware; hexavalent chromium authorization status on DoD work.
• Outgassing or low outgassing processing where your program requires it.
• Packaging: individual bags or trays with caps on, ESD packaging if the connector is filtered or carries components, and no long storage of pre-wired connectors sealed in bags (see the receiving section).
• DFARS counterfeit clauses and any prime contract flow-downs that apply.

Counterfeit and quality risks, and how to receive them

The common failures are not exotic fakes. They are wrong class or key position shipped under a similar number, mixed lots, connectors assembled from piece parts outside the manufacturer's authorization, and pre-wired parts that sat in sealed bags too long.

How DFARS applies. DFARS 252.246-7008 (Jan 2023) defines an electronic part as an integrated circuit, a discrete electronic component such as a transistor, capacitor, resistor or diode, or a circuit assembly, and sets the source order: original manufacturer or its authorized suppliers first, contractor-approved suppliers next, other sources only with written notice to the contracting officer plus inspection, testing and authentication. A plain connector is not named in that definition. Whether your program treats connectors as electronic parts, or applies the same controls by contract or prime policy, is a decision for your contracts and quality staff. Many defense buyers apply the authorized-source rule to connectors either way, and a filtered connector with capacitors inside is closer to the definition than a plain one. Our counterfeit parts avoidance guide covers DFARS 252.246-7007 and AS5553.

At receiving:

• Compare the marking on the shell to the PO, character by character, including class and key position. Check the master keyway position visually against the drawing.
• Match lot or date code on the part, bag label and certificate.
• Check the finish color and plating condition; olive drab and black zinc-nickel look different, and a nickel shell should not be dull or blistered.
• Verify contact count and size against the arrangement, and that contacts are included if ordered.
• For pre-wired connectors, NASA's GSFC advisory NA-GSFC-2003-03 warns that fluoropolymer wire can outgas fluorine that forms hydrofluoric acid in sealed bags and corrodes nickel and gold. Inspect shells and contacts under magnification for darkening.

Our receiving inspection and certs and traceability pages cover the paperwork side.

How we source circular connectors

We do not stock connectors, publish prices or act as an authorized or franchised distributor for any manufacturer. We source the part numbers on your drawing through the manufacturer or its authorized and franchised distributors, with certificates and lot traceability flowed back to you.

• Connectors bought alone, or kitted with contacts, backshells and seal plugs per harness or per assembly.
• Connectors combined with the harness build, machined brackets or GSE fabrication on one purchase order.
• Inactive and hard to find arrangements chased under counterfeit-avoidance controls; see obsolete aerospace parts.
• Your finish restrictions, outgassing requirements and DFARS clauses flowed down in writing.

Related parts: rectangular connectors, aerospace wire and cable, and the electrical parts overview. For cost drivers on a finished assembly, see wire harness cost.

Request circular connectors or a kit

Send your parts list through the harness and connector quote form with full part numbers, quantities, approved sources and any finish or outgassing limits. Those details decide which sources can supply the part under your contract. A person replies within one business day, and every order ships with a certificate of conformance. Drawings on defense and launch programs are often controlled; read how we handle files and controlled programs before sending them.

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Part, quantity and date are enough to start. Drawings and the mutual NDA follow by reply, and controlled programs never send technical data through this site.

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Related

• Sourcing Aerospace Wire Harnesses and Cable Assemblies
• What an Aerospace Wire Harness Costs, and Why
• How to Buy Obsolete Parts Without Buying Counterfeits
• Aerospace Rectangular Connectors: D-Sub, Micro-D, Nano and Rack and Panel

Sources

• Glenair, D38999/20 Series III QPL part number development (rev 03.11.25)
• NASA NEPP Parts Selection List, MIL-DTL-38999 Series I and II
• NASA NEPP, MIL-DTL-38999 Series III and IV application notes
• NASA NEPP, cadmium plating prohibition
• NASA NEPP, zinc plating prohibition
• Amphenol, black zinc-nickel qualified to MIL-DTL-38999 Series III Class Z
• EverySpec, MIL-DTL-38999M Amendment 2 (8 Sep 2017)
• EverySpec, MIL-DTL-26482H Amendment 2 (21 Jun 2013)
• EverySpec, MIL-DTL-5015H Notice 1, cancelled and superseded by SAE AS50151
• EverySpec, MIL-DTL-83723G (7 Dec 2009)
• Acquisition.gov, DFARS 252.246-7008 Sources of Electronic Parts
• Acquisition.gov, DFARS 252.223-7008 Prohibition of Hexavalent Chromium