Low Mating Force Rectangular Connectors MIL-DTL-55302 · B³ Brush Contact
Rectangular board-level connectors that join board to board and wire to board. As an authorized Amphenol distributor, ADMTEC supplies all four body styles — MB, DB, I/O and PC — and their accessories in Korea.
MIL-DTL-55302
What Low Mating Force means
Rectangular board-level connectors whose contacts sit on a .100 inch square grid. The US military specification MIL-DTL-55302 governs the family, and military part numbers begin with M55302.
The name is the point — this family is defined by how little force it takes to mate. Amphenol uses the B³ brush contact as the standard contact, and average engaging and separating force is at most 1.5 ounces per contact, so even high contact counts stay manageable by hand.
The manufacturer states the family has been in service for over 25 years, with more than 50 million brush contacts fielded.
- Specification
- MIL-DTL-55302 (M55302/166~/172)
- Business unit
- Amphenol Aerospace
- Contact system
- B³ brush contact
- Contact grid
- .100 inch square (center to center)
- Rows
- 2 · 3 · 4 rows / 10~100 contacts per row (1-contact steps)
- Body styles
- MB · DB · I/O · PC
- Operating temperature
- −65 ~ +125 °C
The catalogue words the military side as “Military versions meet MIL-DTL-55302/166 through /172”; it never uses qualified or QPL. If your procurement requires QPL listing, tell us and we will confirm it per part number first.
Four Body Styles
Four body styles and how they mate
One standard, four bodies — and each mates only with certain partners. Which of MB, DB, I/O or PC appears on your drawing is the first fork in the road.
Termination and mating partner by body style
| Body style | Also called | Termination | Mates with |
|---|---|---|---|
| MB — Mother Board | Backplane connector | Straight PCB stud or solderless wrap | DB · I/O |
| DB — Daughter Board | Module connector | 90° PCB stud | MB · PC |
| PC — Printed Circuit | Right angle mother board · card extender connector | 90° PCB stud | I/O · DB |
| I/O — Input/Output | Cable connector | I/O-C uses rear release, rear removable crimp contacts (size 22D); I/O-P uses round PCB stud solder contacts | MB · PC |
MB does not mate with PC, and DB does not mate with I/O. Order a pair that does not match and the parts will arrive but will not go together. In practice — DB↔MB joins two boards at right angles, PC↔DB joins them end to end, MB↔I/O-P joins them in parallel (with a spacer), and MB↔I/O-C and PC↔I/O-C bring discrete wires to a board.
- Contact removal direction differs by style
MB, DB and PC use front release, front removable contacts. I/O uses rear release, rear removable crimp contacts (size 22D) or PCB pins. The tooling and the direction of work differ, so confirm before ordering.
Hybrid configurationsDetails · tap to expand
The same family includes hybrids that mix brush signal contacts with power, coaxial or fibre optic termini. A power strip series with cavities for size 16 or 12 power or coaxial contacts is also available.
Small sizes down to 5 per rowDetails · tap to expand
If you need fewer than 10 contacts per row, smaller designs go down to 5 per row. Total counts are 10, 12, 14, 15, 16, 18, 20, 21, 24, 27, 28, 32 and 36, all on the same .100 inch square grid.
Part Number
Two part numbering systems
The same part carries a military number (M55302/…) and a commercial number (MB2-120P-(703)).
Military part number — M55302/166A10X1
- M55302/166A10X1① Specification — MIL-DTL-55302 Low Mating Force rectangular connectors
- M55302/166A10X1② Body type · termination — MB-P (Mother Board, PCB termination). /167 = MB-W (solderless wrap) · /168 = PC · /169 = I/O · /170 = DB
- M55302/166A10X1③ Number of rows — 2 rows. B = 3 rows · C = 4 rows
- M55302/166A10X1④ Contacts per row — 10 per row → 20 total. Written as two digits from 10 to 100, with 00 standing for 100
- M55302/166A10X1⑤ Tail length — .300 ±.025 for MB-P. In the same position W = .222 · Y = .145 · Z = .113 (the code values differ by body style)
- M55302/166A10X1⑥ Tail finish — Tin-lead per MIL-P-81728 (50 to 70% tin), .0001 min. over copper. 2 = gold per MIL-G-45204 type II over nickel per QQ-N-290
Commercial part number — MB2-120P-(703)
- MB2-120P-(703)① Body type — Mother Board. DB = Daughter Board · I/O = Input/Output · PC = Printed Circuit
- MB2-120P-(703)② Number of rows — 2 rows. 3 and 4 rows sit in the same position
- MB2-120P-(703)③ Total contacts — Total, not per row. With 2 rows that is 60 contacts in each row
- MB2-120P-(703)④ Termination — Straight PCB stud. W = solderless wrap · C = crimp (rear removable, size 22D wire well)
- MB2-120P-(703)⑤ Variation suffix — Au/Ni plating plus a PCB stud stickout of .145, MB-P. Look your number up in the table below
🔴 The two systems count contacts differently. The digits in a military number are contacts per row; the digits in a commercial number are the total. A 2-row connector with 60 contacts per row (120 total) is M55302/166A60… as a military number and MB2-120P as a commercial one. Copying the digits across without converting is off by a multiple.
Commercial standard termination codes — default stickout and plating by body style6 rows · tap to expand
| Code | Termination | Stickout · plating |
|---|---|---|
| MBx-xxxP | Straight PCB stud | .021 dia. · .113 ±.025 · Sn/Ni |
| MBx-xxxW | Solderless wrap | .025 sq. · .507 ±.025 · Sn/Ni |
| DBx-xxxP | 90° PCB stud | .021 dia. · .085 ±.025 · Sn/Ni |
| IOx-xxxC | Crimp (rear removable, size 22D wire well) | Sn/Ni |
| IOx-xxxP | PCB stud | .021 dia. · .145 ±.025 · Sn/Ni |
| PCx-xxxP | 90° PCB stud | .021 dia. · .095 (+.035 / −.025) · Sn/Ni |
Plating abbreviations — Sn/Ni is tin over nickel, Au/Ni is gold over nickel, Au/Cu is gold over copper, SnPb/Cu is tin-lead over copper. A variation suffix overrides the defaults given in the standard termination codes.
Contact Arrangements
How many contacts are available
From 10 to 100 contacts per row, in single-contact steps. The total is therefore the row count multiplied out — 20 to 200 for 2 rows, 30 to 300 for 3 rows, 40 to 400 for 4 rows, and the same across all four body styles.
For fewer than 10 contacts per row there is a separate small-size range covering totals from 10 to 36. 🔴 Within that range, 18 and 24 contacts are not uniquely specified by the total alone — 18 exists as 2 rows × 9 and as 3 rows × 6, 24 as 3 rows × 8 and as 4 rows × 6, and the body dimensions and board hole patterns differ. For those two, please give us the row count as well.
Small sizes — row configurations for totals of 10 to 3613 rows · tap to expand
| Total contacts | Contact pattern |
|---|---|
| 10 | 2 rows × 5 |
| 12 | 2 rows × 6 |
| 14 | 2 rows × 7 |
| 15 | 3 rows × 5 |
| 16 | 2 rows × 8 |
| 18 | 2 rows × 9 or 3 rows × 6 |
| 20 | 4 rows × 5 |
| 21 | 3 rows × 7 |
| 24 | 3 rows × 8 or 4 rows × 6 |
| 27 | 3 rows × 9 |
| 28 | 4 rows × 7 |
| 32 | 4 rows × 8 |
| 36 | 4 rows × 9 |
When converting contacts per row into a commercial number, multiply by the row count — 3 rows × 40 contacts is IO3-120.
Variation Suffix
What the three digits in brackets mean
The (700) style suffix at the end of a commercial part number specifies plating, stickout and rear treatment. Look up the number on your drawing directly.
Variation suffixes (700) to (773) — plating · stickout · rear treatment66 rows · tap to expand
| Suffix | What it specifies |
|---|---|
| (700) | Gold plate per MIL-G-45204 type II — .000030 min. gold (.000050 for solderless wrap) over .000050 min. nickel. Standard termination length |
| (701) | Gold plate per MIL-G-45204 type II — .000050 min. gold over .00015 min. copper. Standard termination length |
| (702) | Straight PCB stud .145, Sn/Ni — MB-P |
| (703) | Straight PCB stud .145, Au/Ni (same as 700) — MB-P |
| (704) | Straight PCB stud .145, Au/Cu (same as 701) — MB-P |
| (705) | 90° PCB stud .120, Sn/Ni — DB |
| (706) | 90° PCB stud .120, Au/Ni (same as 700) — DB |
| (707) | 90° PCB stud .120, Au/Cu (same as 701) — DB |
| (709) | PCB stud — DB (90°) .300 · MB-P .300 · IO-P .335, Sn/Ni |
| (710) | Solderless wrap .025 sq., stickout .665, Sn/Ni — MB-W |
| (711) | Solderless wrap .025 sq., stickout .665, Au/Ni (same as 700) — MB-W |
| (713) | PCB stud .060, Sn/Ni — IO-P |
| (714) | 90° PCB stud .150, Sn/Ni — PC · DB |
| (715) | Solderless wrap .025 sq., stickout .665, Au/Cu (same as 701) — MB-W |
| (716) | 90° PCB stud .085, matte tin — DB |
| (717) | 90° PCB stud .095, matte tin — PC |
| (718) | 90° PCB stud .120, matte tin — DB |
| (719) | PCB stud — MB-P .300 · IO-P .335, matte tin |
| (720) | PCB stud .060, matte tin — IO-P |
| (721) | PCB stud .500, Sn/Ni — IO-P |
| (722) | Straight PCB stud .356, matte tin — MB-P |
| (723) | Straight PCB stud .192, Sn/Ni — MB-P |
| (724) | 90° PCB stud .095, RTV potted rear, Sn/Ni — PC |
| (725) | 90° PCB stud .120, RTV potted rear, Sn/Ni — DB |
| (726) | 90° PCB stud .150, RTV potted rear, Sn/Ni — PC · DB |
| (727) | Straight PCB stud .145, RTV potted rear, Sn/Ni — MB-P |
| (728) | Straight PCB stud .145, Au/Ni (same as 700), RTV potted rear — MB-P |
| (729) | 90° PCB stud .120, Au/Ni (same as 700), RTV potted rear — DB |
| (730) | 90° PCB stud .150, Au/Ni (same as 700) — PC · DB |
| (731) | Straight PCB stud .145, matte tin — MB-P |
| (732) | PCB stud — DB (90°) .300 · MB-P .300 · IO-P .335, Au/Cu (same as 701) |
| (733) | Straight PCB stud .421, matte tin — MB-P |
| (734) | Solderless wrap .025 sq., stickout .665, Au/Ni (same as 700), RTV potted rear — MB-W |
| (735) | RTV potted rear, standard termination length, Au/Ni (same as 700) |
| (736) | RTV potted rear, standard termination length, Sn/Ni — use (724) for PC |
| (737) | PCB stud — DB (90°) .300 · MB-P .300 · IO-P .335, Au/Ni (same as 700), RTV potted rear |
| (738) | Straight PCB stud .192, SnPb/Cu (Mil-Spec) — MB-P |
| (739) | PCB stud — DB (90°) .300 · MB-P .300 · IO-P .335, RTV potted rear, Sn/Ni |
| (740) | Solderless wrap .025 sq., stickout .665, Sn/Ni, RTV potted rear — MB-W |
| (741) | Solderless wrap .025 sq., stickout .280, Au/Ni (same as 700) — MB-W |
| (742) | Straight PCB .145, Au/Ni (same as 700), epoxy potted rear — MB-P |
| (743) | 90° PCB .120, Au/Ni (same as 700), epoxy potted rear — DB |
| (744) | 90° PCB .120, Au/Ni (same as 700, Mil-Spec), epoxy potted rear — DB |
| (746) | 90° PCB .120, SnPb/Cu (Mil-Spec), epoxy potted rear — DB |
| (747) | PCB stud .200, Sn/Ni — IO-P |
| (748) | Straight PCB stud .145, Sn/Ni, epoxy potted rear — MB-P |
| (749) | PCB, epoxy potted rear, standard termination length, Sn/Ni |
| (750) | PCB stud .172 termination, Au/Ni (same as 700), RTV potted rear — MB-P |
| (751) | 90° PCB stud .150, Sn/Ni, epoxy potted rear — PC |
| (752) | Au/Ni, epoxy potted rear, standard termination length |
| (753) | Solderless wrap .025 sq., stickout .665, Au/Ni (same as 700), epoxy potted rear — MB-W |
| (754) | PCB stud .172 termination, SnPb/Cu (Mil-Spec) — MB-P |
| (757) | PCB stud .391, matte tin — MB-P |
| (758) | PCB stud .172, Au/Ni (same as 700), epoxy potted rear — MB-P |
| (760) | PCB stud .192, Au/Ni (Mil-Spec) — MB-P |
| (761) | 90° PCB stud .120, Sn/Ni, epoxy potted rear — DB |
| (762) | PCB stud .145, Au/Ni (Mil-Spec), epoxy potted rear — MB-P |
| (763) | PCB stud .145, SnPb/Cu (Mil-Spec), epoxy potted rear — MB-P |
| (764) | 90° PCB stud .150, SnPb/Cu (Mil-Spec), epoxy potted rear — DB · PC |
| (765) | PCB stud — DB (90°) .300 · MB-P .300, SnPb/Cu (Mil-Spec), epoxy potted rear |
| (766) | 90° PCB stud .120, Au/Ni (Mil-Spec), epoxy potted rear — DB |
| (767) | PCB stud .192, Au/Ni (Mil-Spec), epoxy potted rear — MB-P |
| (768) | PCB stud .172, Au/Ni (Mil-Spec) — MB-P |
| (769) | 90° PCB stud .200, Au/Ni (Mil-Spec) — DB |
| (770) | 90° PCB stud .260, Au/Ni (Mil-Spec) — DB |
| (773) | 90° PCB stud .150, Au/Ni (Mil-Spec), RTV potted rear — PC · DB |
The numbering is not continuous — (708), (712), (745), (755), (756), (759), (771) and (772) do not appear in the catalogue. If the number on your drawing is not in this table, tell us. Stickout values refer to the J dimension on each connector drawing.
Performance
Ratings and materials
Electrical and mechanical ratings
| Item | Value |
|---|---|
| Contact current rating | 3 A for PCB contacts · 5 A for solderless wrap / crimp contacts |
| Voltage rating | Sea level 1300 · 70,000 ft 325 |
| Operating temperature | −65 ~ +125 °C |
| Insulation resistance | 5 GΩ minimum |
| Contact engaging · separating force | 1.5 oz maximum average per contact |
| Polarization | Up to 256 keying combinations |
The voltage rating is printed in the catalogue as bare numbers with no unit symbol, so it is reproduced as printed. Contact resistance is not listed here because the catalogue only states that it “varies depending on the point of measurement and the length of the contact” — ask us and we will confirm it per part number.
Materials and finishes6 rows · tap to expand
| Part | Material · specification |
|---|---|
| Connector body | Glass-filled thermoplastic — MIL-M-24519 type GPT-15F and/or Grade B, MIL-P-46161 Class 15 (UL94V-O) |
| Polarization keys | Glass-filled acetal — MIL-P-46137 |
| Locking screw · mounting bushing | Corrosion resistant steel, AISI 300 types, passivated per QQ-P-35 |
| Contact holders | Copper alloy — QQ-B-626 or SAE J463 |
| Contact wire | Beryllium copper — ASTM B197 |
| Sleeves (where applicable) | Stainless steel AMS-5514, passivated per ASTM A967 |
RoHS compliant versions are available separately. Let us know your requirement.
Identification
Reading the markings, rows and cavity numbers
- A body marked Bendix is still the genuine part
The catalogue states it plainly — the former brand name Bendix may still appear moulded into the body, and it is replaced with the Amphenol name as the moulds are remade. Do not reject incoming inspection on the marking alone.
Rows start at A, at the radius endDetails · tap to expand
Row letters and cavity numbers are moulded into the body. Row identification always starts at the radius end and begins with row A. Cavity numbering also starts at the radius end, begins at cavity 6 and is then marked every fifth cavity. Arrangements with 10 contacts per row carry no numerals at all, and up to 9 contact locations at the high numeral end are left unmarked.
Which face is marked depends on the body styleDetails · tap to expand
MB and PC carry row letters on both the front and rear faces, with cavity numbers on the rear. DB carries rows and cavities on the front face; I/O carries both on the rear.
- Contacts come installed
MB, DB, I/O and PC are all supplied with contacts assembled as ordered. Receiving them without contacts requires a specific call-out.
Details · tap to expand
For military I/O part numbers, a last digit of 3 means the connector is supplied less contacts. Replacement crimp contacts are then ordered separately as M55302/171-1 (tin-lead) or M55302/171-2 (gold).
Accessories
Bushings · screws · polarization keys
🔴 Connectors ship less accessory items. Mounting bushings, locking screws and polarization keys are separate line items — order the connector alone and you will have nothing to fasten it with. Mounting bushings are 2 per connector, and polarization keys, if used, are 4 per connector half (8 for a mated pair).
Accessory part numbers — 8 items, military and proprietary8 rows · tap to expand
| Accessory | Series | Military P/N | Proprietary P/N | Qty required |
|---|---|---|---|---|
| Polarization keys | MB · DB · I/O · PC | M55302/78-02 | 10-285422-2 | 4 |
| Locking / mounting bushing | MB | M55302/172-01 | 10-411196-3 | 2 |
| Alternate length bushing (longer) | MB | M55302/172-02 | 10-411196-5 | 2 |
| Locking bushing | PC | M55302/172-05 | 10-411196-4 | 2 |
| Locking screw, plain | I/O | M55302/172-04 | 10-502599 | 2 |
| Locking screw, slotted | I/O | — | 10-502599-1 | 2 |
| Locking screw, slotted (low profile) | I/O | M55302/172-03 | 10-502599-2 | 2 |
| Test probe kit | MB · DB · I/O · PC | — | 11-10400-22 | 1 |
- Polarization keys — up to 256 combinations
There are four key positions and four possibilities at each, giving 256 combinations. Both halves of a mated pair must be specified to the same code.
Details · tap to expand
A code is written as a mix of letters and numbers, such as B, H–1, 5. If the letters and numbers on the facing connectors correspond, the pair mates; if not, it physically will not go in. The flat side of each key faces the letter or number designation.
- The body is deliberately non-rigid
The body is designed to be non-rigid so it can absorb board compliance, vibration and differential expansion. For maximum performance, hold the mating surface straight to within 0.010 inch during assembly.
Details · tap to expand
No external board support is generally required as long as the mounting surface is rigid enough. For longer installations, consider external support to prevent excessive flexing of the connector and board assembly.
The test probe kit confirms that contacts are correctly wired and, just as importantly, prevents damage to the brush contacts while probing — do not probe them with an ordinary test probe (the manufacturer recommends one kit per connector gender). PC style is the exception to the rule above: it ships with PC tail combs fitted, protecting the tails in transit and aligning the contacts during board assembly.
Q&A
Frequently Asked Questions
My connector is marked Bendix — is it genuine?
Yes. The manufacturer's catalogue says so directly: this family may still carry the former brand name Bendix moulded into the body, and it is replaced with the Amphenol name as the moulds are remade. If your incoming inspection checks markings, you can cite that statement, and we will supply confirming documentation alongside the C of C.
The drawing only says MB4-160P-(703). What part is that?
A Mother Board connector, 4 rows, 160 contacts in total (40 per row), straight PCB stud termination, with (703) calling out gold over nickel plating and a PCB stud stickout of .145. Accessories are not included, so order 2 mounting bushings with it — and 4 polarization keys if you use them.
Should I quote the military number or the commercial one?
Either, exactly as it appears. Just be careful when converting between them: the digits in a military number are contacts per row, while the digits in a commercial number are the total. A 2-row connector with 60 contacts per row is M55302/166A60… as a military number and MB2-120P as a commercial one. If in doubt, send us a photo of the drawing.
I only know it has 18 contacts. Is that enough to identify it?
Not for 18 or 24. Eighteen contacts exists as 2 rows × 9 and as 3 rows × 6; twenty-four exists as 3 rows × 8 and as 4 rows × 6, and the body dimensions and board hole patterns differ. Please give us the row count as well, or send a photo of the markings on the existing part.
Do the bushings, screws and keys come with the connector?
No. This family ships less accessory items. Mounting bushings are 2 per connector, and polarization keys are 4 per connector half if you use them. Both military and proprietary part numbers exist, so send us either, and we will confirm them together with the connector in one go.
Can I take delivery without contacts and fit them later?
For the I/O style, yes. A last digit of 3 on the military part number supplies the connector less contacts, and replacement crimp contacts are then ordered as M55302/171-1 (tin-lead) or M55302/171-2 (gold). MB, DB and PC are supplied with contacts assembled as ordered.
Is a Certificate of Conformance included?
Yes, with every order — see the authorized distributor certification page for what it covers and for the original certificate.
Specification sources2 documents · tap to expand
Specifications · ordering · accessory part numbers: Amphenol Aerospace, Low Mating Force Rectangular Connectors catalogue section (36 pp., printed pp. 60–95) · Manufacturer: Amphenol Aerospace. We confirm the latest revision and the exact applicable specification with you when we quote.