MIL-DTL-24308 D-Sub Connectors:
Complete Guide to M24308 Part Numbers, Classes & Cross-Reference

What MIL-DTL-24308 Is — and Why "Non-Environmental" Matters

MIL-DTL-24308 is the U.S. military specification for rectangular, polarized-shell, D-subminiature connectors used in rack-and-panel, cable-to-cable, and cable-to-board applications. It is issued and maintained by DLA Land and Maritime, was formerly catalogued as MIL-C-24308, and its full title is worth reading carefully because it defines the limits of the family: Connectors, Electric, Rectangular, Non-Environmental, Miniature, Polarized Shell, Rack and Panel.

The commercial world knows the same interface as IEC 60807-3 / DIN 41652 — the generic D-Sub. The connector itself was invented by James D. Cannon in the late 1950s as a smaller, denser alternative for the then-new computer industry, named for its D-shaped trapezoidal shell, and Cinch was the first company to license it. Sixty-plus years later it remains one of the most widely multi-sourced interfaces ever standardized, which is exactly why it is still the default choice for avionics LRU racks, ground support equipment, and instrument backplanes.

Test methods for the specification are drawn from EIA/ECA-364. The current baseline revision is Revision G, under which the legacy MS18269–MS18276 detail sheets have been progressively cancelled and consolidated into the modern M24308/1 through M24308/24 slash-sheet series.

The word non-environmental is the single most misunderstood part of the spec. The base D-Sub is not a sealed connector — there is no interfacial seal, no environmental backshell requirement, and no immersion rating. If your application involves moisture, washdown, or pressure differentials, either specify a supplier's sealed/hermetic variant (see the sealing section below) or step up to a circular connector such as MIL-DTL-38999.

Shell Sizes and Contact Counts

Shell size is the first number a buyer looks at, because it drives contact count, panel cutout, and whether the connector physically fits the rack slot. Standard-density D-Subs use size-20 contacts; high-density versions pack size-22 contacts into the same shell envelope.

Note that the commercial names are frequently misused: a "DB-25" is shell size 3, while a DE-9 is shell size 1. Track the MIL shell number and the contact population separately — a 9-position DE and a 15-position DE share a shell but not a panel footprint for wiring.

Reading an M24308 Part Number

An M24308 part number has four informational blocks. Take M24308/2-1F as the example:

• M24308 — the governing specification (non-environmental rectangular miniature polarized-shell rack-and-panel)
• /2 — the slash sheet, which defines the connector style: shell/mounting configuration, contact gender, and termination method
• -1 — the dash number, which encodes shell size and insert arrangement (dash 1 through 5 map to shell sizes 1 through 5 in the standard-density layouts)
• F — the trailing letter, which designates the shell finish (see the finish-code table below)

The slash sheet is what most cross-reference errors get wrong, so it is worth knowing the main families by heart:

Shell Finish Codes

The trailing letter is a finish designator, not a gender or a mounting code. Two of the most common under Class G and Class N are A (pure electrodeposited aluminum) and K (zinc-nickel), with cadmium and tin-lead finishes appearing elsewhere in the family. Finish codes are class-dependent — always confirm the trailing letter against the applicable slash sheet rather than assuming a finish because a distributor listing carried the same letter. For the corrosion and conductivity trade-offs behind each plating, see our connector plating guide.

Classes: What the Letter G, N, M or D Actually Means

A common misreading is that the class letter denotes an environmental rating. It does not — it denotes the finish and application class:

Separately, the hermetic D-Sub family uses its own class letters for the glass-to-metal sealed versions — Class H (carbon steel shell, tin-lead plated over nickel underplating) and Class K (304L stainless steel shell, dull nickel plated), both with vitreous glass insulators. These are the variants you specify when the connector has to pass through a pressurized bulkhead or a vacuum boundary.

The N/M distinction is where sourcing projects most often stall: a non-magnetic D-Sub is not a plating option, it is a different bill of materials. If your drawing calls out a Class N part, substituting a Class G equivalent — however good the plating — invalidates the requirement.

Electrical and Mechanical Specification

Two traps sit in this table. First, hermetic D-Subs are derated — the glass seal limits per-contact current to roughly 5 A regardless of what the crimp-contact table says. Second, the headline 40 A figures you see in some catalogs refer to Combo-D mixed-layout connectors with High Efficiency Power (HEP) contacts, not to the size-20 signal contacts in a standard-density insert. Combo-D lets you put signal, power, and coax in one D-shaped shell, but it is a mixed-technology product, not a MIL-DTL-24308 standard-density part.

For the test methods behind these numbers — dielectric withstanding voltage, insulation resistance, and low-level contact resistance — see our DWV / IR / contact resistance testing guide.

Termination Options

Mating the same shell family with removable crimp contacts in one position and solder cups in another is possible on some vendor lines, but do not assume it: the slash sheet fixes the termination for a given part number.

The Sealing Question — When a D-Sub Is the Wrong Answer

Because the base specification is explicitly non-environmental, sealing is a supplier extension rather than a spec guarantee. Three common upgrade paths exist:

• Hermetic (glass-to-metal) receptacles — Class H and Class K above; the correct choice for pressurized bulkheads, vacuum chambers, and fuel-tank penetrations, at the cost of a lower per-contact current rating
• EMI/RFI filtered D-Subs — the same shell with capacitive filter elements (C, L, Pi, or T topology) built into the insert, used when the shield termination of a standard connector is not enough to meet a radiated-emissions limit
• Sealed rectangular variants from individual suppliers — gasketed, IP-rated D-shell products that are contract-specific, not spec-defined

If the requirement is sustained immersion, washdown, or an IP67-and-above environmental rating, a rectangular D-shell is the wrong architecture. Move to a circular connector or a purpose-built sealed rectangular product. Our IP rating guide covers where the IP67 / IP68 / IP69K boundaries actually fall.

D-Sub vs Micro-D vs Nano-D vs Circular

Rectangular high-density connectors are not a single family. The pitch — not the shell shape — decides which one you are looking at:

The engineering rule is straightforward: stay with D-Sub when the interface is a rack, a panel, or a board and the environment is benign. Move to Micro-D or Nano-D when board space and weight dominate and the harness is short. Move to circular when the connector must survive moisture, salt spray, or sustained vibration. The comparison between the two most confusable families is covered in our MIL-DTL-38999 vs MIL-DTL-83513 guide.

Manufacturer Cross-Reference: Who Builds MIL-DTL-24308

Cross-referencing a D-Sub is not a shell-size lookup. Four attributes must match before a substitute is valid: slash sheet (shell style, contact gender, termination), shell size and insert arrangement, class (G vs N vs M vs D — finish and magnetics), and contact termination (crimp vs solder cup vs PC tail). Get all four right and the part drops in; miss one and the harness will not build. Our complete connector cross-reference guide covers the full mapping methodology.

Airoadcon MIL-DTL-24308 Product Line

Airoadcon manufactures MIL-DTL-24308 polarized-shell D-Subminiature connectors in the standard-density Class G configurations — M24308/1-xF, M24308/2-xF and M24308/4-xF part numbers across shell sizes 1 through 5 (DE / DA / DB / DC / DD), with size-20 gold-over-nickel crimp contacts, 500 mating cycles, and a −55°C to +125°C operating range. Individual part-number pages with full specifications and cross-reference data are listed under our MIL-DTL-24308 product section, and higher-density requirements are served by our Micro-D (MIL-DTL-83513) line.

MIL-DTL-24308 Selection Checklist

• Confirm the environment first. The base spec is non-environmental. If the connector sees moisture or pressure, you need a hermetic or supplier-sealed variant — or a circular connector.
• Pin the slash sheet. /2 is a socket receptacle, /4 is a pin plug, /6 and /8 are the non-magnetic equivalents. The slash sheet also fixes the termination.
• Decode the dash number. Dash 1–5 maps to shell sizes 1–5; verify the insert arrangement rather than assuming the contact count from the shell size.
• Read the trailing letter as a finish — A and K are common, and finish codes are class-dependent. Never assume from an equivalent distributor listing.
• Check the class. Class N (non-magnetic) and Class M (non-magnetic, space) are different bills of materials, not plating options.
• Confirm current rating — 7.5 A per size-20 contact non-hermetic, roughly 5 A hermetic. Do not read Combo-D power ratings across to a standard-density insert.
• Match the termination — crimp for production and repair, solder cup for prototypes, PC tail for backplanes.
• Specify the accessory — #4-40 jackscrews, slide-latch hardware, hoods, and backshells sized to the shell and cable bundle.